Fluid distribution and collection in landfills and contaminated sites

ABSTRACT

A fluid injection and removal system to inject or remove fluids from a landfill or contaminated area. The system allows for treatment of waste in the landfill or the contaminated area. The fluid injection and removal system includes a permeable layer and at least one perforated pipe. The permeable layer enables essentially uniform distribution of the fluid into the underlying waste or contaminated area. The fluid injection and removal system can be combined with a leachate collection system to create a leachate recirculation system for use in a landfill. The leachate collection system includes at least one perforated collection pipe embedded in a drainage layer. Sensors can be provided in the permeable layer to enable the change in the physical characteristics of the waste adjacent the permeable layer to be monitored.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional Application Ser. No.60/599,623, filed Aug. 6, 2004

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

STATEMENT REGARDING GOVERNMENT RIGHTS

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fluid distribution and optionallycollection in solid waste in landfills; and particularly bioreactivelandfills and contaminated sites. In one aspect, the present inventionrelates to waste treatment liquid collection and recirculation in solidwaste in landfills. In another aspect, the present invention relates toremediation of contaminants in the contaminated liquid or contaminatedsubsurface. In both instances, layer of a permeable, hydraulicallyconductive material is provided to allow the distribution of the fluidsinto the layer and from the layer into the landfill or contaminatedsite. The invention also relates to the use of sensors in the layer tocollect data about the surrounding area.

2. Description of Related Art

The key difference between a “dry tomb” landfill and a bioreactorlandfill is that bioreactor landfills require controlled addition ofleachate or moisture to the solid waste in the landfill. Therecirculation of leachate, other liquids, or fluids (e.g., steam, air)to the solid waste in the landfill is a major component in bioreactorlandfills. The addition of leachate or moisture increases wastedecomposition. Environmental and economical benefits of leachaterecirculation for municipal solid waste landfills or bioreactorlandfills are well documented. These benefits include a reduction in theleachate treatment and disposal costs, accelerated decomposition andincreased settlement of waste resulting in an airspace gain, an increasein the rate of gas production, acceleration in the generation oflandfill gas and which results in a potential for higher short-termrevenues from a gas-to-energy system, reduction in the risk associatedwith contamination during off-site transportation, treatment, anddisposal of leachate and potential reduction in the post-closure careperiod and maintenance costs. Risks and drawbacks of leachaterecirculation include, a potential decrease in the slope stability oflandfills, a potential increase in the leachate head on the liner, ifleachate collection system is not designed to efficiently drain injectedand recirculated leachate, potential flooding of the gas collectionsystem, and possible leachate seepage from the landfill side slopes, ifan adequate buffer distance is not maintained.

The most common leachate recirculation techniques are broadly dividedinto surface and subsurface applications. Surface applications includedirect application of leachate or spray irrigation of leachate on thelandfill surface and surface ponding of leachate. Climate dependency,odor problems, interference with daily operations, poor aesthetics, andpotential runoff of applied leachate into storm water management systemare the drawbacks of surface application techniques. Conventionalsubsurface application methods include vertical wells and horizontaltrenches. Horizontal trenches are most commonly used in relatively new,municipal solid waste landfills. It is most cost effective to installhorizontal trenches before the landfill is capped at the designelevation in the landfill cell. Vertical wells can interfere withlandfill daily operations. However, vertical wells can be installedafter a landfill is capped or can be retrofit into existing landfills.Therefore, vertical wells are most commonly used in retrofit landfillsor where implementing horizontal trenches is not feasible or costeffective. Disadvantages and limitations of vertical wells andhorizontal trenches include odor problems during installation due toexcavation of waste, high capital cost of construction; and non-uniformdistribution of leachate due to the formation of “dry zones” or “drypockets” where injected leachate cannot reach. Such dry zones can reducethe quantity and rate of landfill gas generated. The dry zones can alsolead to differential settlement of waste which can result in greaterlandfill cap maintenance costs. In addition, the amount of leachate thatcan be recirculated by these methods may not be sufficient to get rid ofall leachate typically produced by landfills located in humid regions.

The related patent art for municipal solid waste sites is evidenced byU.S. Pat. Nos. 5,855,664 to Bielecki et al and 6,599,058 to Arnold.

There remains the need for a system and method of distributing andcollecting fluids from a portion of a landfill or contaminated sitewhich allows for uniform distribution of the fluid into the landfill orcontaminated site and which is economical and easy to install.

SUMMARY OF THE INVENTION

A fluid injection and removal system for use in solid waste landfill,landfill cell or contaminated area. The system allows for the injectionof fluids and the removal of fluids from a landfill, landfill cell orcontaminated area. The system also allows for treatment or remediationof the waste in the landfill or the contaminated area (or subsurface) orthe ground water removed from or injected into the landfill orcontaminated area. The fluid injection and removal system includes apermeable layer and at least one perforated pipe. The permeable layerand perforated pipe are in fluid communication. The permeable layer isconstructed of a permeable material having a hydraulic conductivitygreater than the hydraulic conductivity of the underlying waste orcontaminated area. The permeable layer enables essentially uniformdistribution of the fluid injected into the permeable layer into theunderlying waste or contaminated area. The permeable layer can be ageocomposite drainage layer. The permeable layer can be constructed ofan inert or reactive material. Use of a reactive material allows fortreatment of the fluid as it passes through the permeable layer. Thefluid injected into the landfill can be used to accelerate thedecomposition of the waste such as in a bioreactive landfill. The fluidcan include a surfactant which helps to reduce the concentration ofcontaminants in the underlying waste or contaminated area. The fluidinjection and removal system can be combined with a leachate collectionsystem to create a leachate recirculation system for use in a landfillor landfill cell. The leachate collection system includes at least oneperforated collection pipe embedded in a drainage layer. The leachatecollection system may also include a liner.

To use the fluid injection and removal system, the permeable layer ispositioned on the surface of the waste or contaminated area. Theperforated pipe is then positioned within or immediately outside thepermeable layer on a side opposite the waste or contaminated area.Additional waste or soil can then be positioned on the top of thepermeable layer and perforated pipe. Several fluid injection and removalsystems can be used in a single landfill at different elevations. Whenthe fluid injection and removal system is used as part of a leachaterecirculation system, the leachate collection system is placed at thebottom of the landfill. Once the fluid injection and removal system isinstalled, the fluid is injected into the perforated pipe and into thepermeable layer. The fluid moves through the permeable layer into theunderlying waste or contaminated area. If the fluid injection andremoval system is part of the leachate recirculation system, liquidmoves from the perforated pipe, through the permeable layer and downthrough the waste to the collection pipe of the leachate collectionsystem. The collected leachate is then removed from the leachatecollection system. The collected leachate can be injected again into thewaste using the fluid injection and removal system. To use the fluidinjection and removal system to remove gases or vapors, gases or vaporsfrom the waste move into the same perforated pipe that is used for thefluid injection or a separate devoted perforated pipe or pipes can beused. A vacuum or gravity driven system connected to the perforated piperemoves the gases or vapors from the perforated pipe.

Sensors can be provided in the permeable layer to estimate the physicalcharacteristics or the change in the physical characteristics of thewaste or contaminated area adjacent the permeable layer to be monitored.The data from the sensors can be used to increase the efficiency of thelandfill or to assist in the design of more efficient landfills.

The present invention relates to a method for injecting a wastetreatment fluid or any fluid including water into a portion of solidwaste in a landfill which comprises the steps of: providing a layerconstructed of a permeable material having hydraulic conductivity, andhaving a first surface and an opposed second surface, and a perforatedpipe positioned adjacent the layer, wherein the layer is positioned onthe portion of the solid waste of the landfill so that the secondsurface of the layer is adjacent to and above the portion of solidwaste; and injecting the fluid into the perforated pipe under positivepressure so that the fluid exits the pipe and travels into and throughthe layer and is distributed into the portion of solid waste adjacentthe layer.

Further, the present invention relates to a method for installing afluid injection system into a portion of solid waste in a landfill whichcomprises the steps of: providing a layer constructed of a permeablematerial having hydraulic conductivity and having a first surface and anopposed second surface forming a plane of the layer; positioning thelayer on the portion of solid waste of the landfill so that the secondsurface of the layer is adjacent the solid waste; and positioning aperforated pipe adjacent the layer.

Still further, the present invention relates to a method of collectingand recirculating waste treatment liquid in a portion of solid waste ina landfill which comprises the steps of: providing a fluid injectionsystem including a layer constructed of a permeable material havinghydraulic conductivity and having a first surface and an opposed secondsurface, a perforated pipe adjacent the layer and a waste treatmentliquid collection system spaced apart from the fluid injection system,wherein the layer is positioned on the portion of the solid waste sothat the second surface of the layer is adjacent to and above theportion of solid waste and the waste treatment liquid collection systemis positioned at a bottom of the portion of solid waste in the landfill;injecting a waste treatment liquid into the perforated pipe underpositive pressure so that the waste treatment liquid moves into andtravels through the layer and is distributed into the portion of solidwaste adjacent the second surface of the layer and wherein the wastetreatment liquid moves down through the portion of the solid wastetoward the waste treatment liquid collection system due to gravity; andcollecting the waste treatment liquid using the waste treatment liquidcollection system after the waste treatment liquid passes through thesolid waste.

Further still, the present invention relates to a method of installing awaste treatment liquid recirculation system in a portion of solid wastein a landfill which comprises the steps of: providing a layer having afirst surface and an opposed second surface constructed of a permeablematerial having hydraulic conductivity and forming a plane of the layer;positioning the layer on the portion of solid waste so that the secondsurface of the layer is adjacent the portion of solid waste in thelandfill; positioning a perforated pipe adjacent the layer; providing awaste treatment liquid collection system; and positioning the wastetreatment liquid collection system in the portion of solid waste spacedpart from and below the layer and perforated pipe.

Further, the present invention relates to a method of installing a wastetreatment liquid recirculation system in a portion of solid waste in alandfill which comprises the steps of: providing a layer having a firstsurface and an opposed second surface constructed of a permeablematerial having hydraulic conductivity and forming a plane of the layer;positioning the layer on the portion of solid waste so that the secondsurface of the layer is adjacent the portion of solid waste in thelandfill; positioning a perforated pipe adjacent the layer; providing awaste treatment liquid collection system; and positioning the wastetreatment liquid collection system in the portion of solid waste spacedpart from and below the layer and perforated pipe.

Further still, the present invention relates to a method for collectingand removing gases from a portion of solid waste of a landfill whichcomprises the steps of: providing a layer constructed of a permeablematerial which allows for gases to flow into the layer and one or moreperforated pipes, the layer having a first surface and an opposed secondsurface and wherein the layer is positioned on the portion of solidwaste in the landfill so that the second surface of the layer isadjacent the solid waste and one or more of the perforated pipes arepositioned adjacent to the layer; providing a suction system connectedto the perforated pipe; moving the gases from the portion of solid wasteadjacent the layer into the layer; and activating the suction system tomove the gases from the portion of solid waste and into the perforatedpipe and to remove the gases from the perforated pipe.

Still further, the present invention relates to a system for injectingfluid into a portion of solid waste in a landfill which comprises: alayer constructed of a permeable material having a hydraulicconductivity and having a first surface and an opposed second surfaceforming a plane of the layer, wherein the layer is configured to bepositioned on the portion of solid waste in the landfill so that thesecond surface of the layer is adjacent the solid waste; and aperforated pipe positioned adjacent the layer parallel to the plane ofthe layer, wherein fluid is injected into the perforated pipe and movesfrom the perforated pipe into the layer and travels through the layerand into the portion of solid waste adjacent the second surface of thelayer.

Further, the present invention relates to a system for collecting andrecirculating waste treatment liquid in a portion of solid waste in alandfill which comprises: a layer constructed of a permeable materialhaving a hydraulic conductivity and having a first surface and anopposed second surface forming a plane of the layer, the layerconfigured to be positioned on the portion of solid waste in thelandfill so that the second surface of the layer is adjacent the solidwaste of the landfill; a perforated pipe positioned adjacent the layerparallel to the plane of the layer; and a waste treatment liquidcollection system including at least one perforated collection pipeembedded in a layer of hydraulically conductive material, wherein thewaste treatment liquid collection system is positioned in the portion ofsolid waste of the landfill adjacent to and spaced apart from the secondsurface of the layer, wherein the waste treatment liquid is injectedinto the layer through the perforated pipe and travels through the layerand is distributed into the solid waste adjacent the second surface ofthe layer and moves downward through the portion of solid waste towardthe waste treatment liquid collection system due to gravity and movesthrough the hydraulically conductive material of the waste treatmentliquid collection system and into the perforated collection pipe.

Finally, the present invention relates to a method for determiningphysical characteristics of a portion of solid waste in a landfill whichcomprises the steps of: providing a layer constructed of a permeablematerial having hydraulic conductivity with a first surface and anopposed second surface and sensors mounted in the layer adjacent thesecond surface and a perforated pipe positioned adjacent the layer,wherein the layer is positioned on the portion of the solid waste of thelandfill so that the second surface of the layer is adjacent to andabove the portion of solid waste; activating the sensors; obtaining datafrom the sensors; and determining from the data, physicalcharacteristics or changes in the physical characteristics of theportion of solid waste adjacent the second surface of the layer.

One of the advantages of the present invention, is that excavation ofwaste is not needed to install and construct the permeable layer.Therefore no odors are released during installation and construction ofthe permeable layer. Another advantage is that installation costs arelower since a single permeable layer can be used in place of multiplehorizontal trenches or vertical wells. Permeable layers also result inrelatively uniform distribution of injected leachate below the permeableLayer which could result in reduction in differential settlement andrelated post-closure maintenance costs. Permeable layers made up ofgranular materials provide an ideal platform to embed sensors formonitoring the pressure, temperature and other physical, chemical, orbiological parameters associated with the migration of injected liquids.Permeable or granular layers offer advantages over conventionalhorizontal trenches including a significant increase in the quantity ofleachate that can be recirculated per unit mass of waste. A permeablelayer is hydraulically more efficient than horizontal trenches atuniformly wetting the underlying waste. Permeable layers can achieverelatively uniform distribution of moisture (or leachate) which reducesdry pockets and reduces differential settlement of the waste. Use of apermeable layer also increases the gas production rate of the waste.

The substance and advantages of the present invention will becomeincreasingly apparent by reference to the following drawings and thedescription.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic cross-sectional front view of a leachaterecirculation system 130 in waste 100 in a landfill 110.

FIG. 1B is a schematic cross-sectional front view of the fluid injectionand removal system 10 showing the permeable layer 12, the perforatedpipe 16 and the sensors 40.

FIG. 2 is a schematic plan view of a fluid injection and removal system10 showing the permeable layer 12, the perforated pipe 16 and the pump18, the flow gauge 24, the pressure gauge 22, the control valve 20 andthe sensor locations.

FIG. 3 is a schematic cross-sectional front view of a fluid injectionand removal system 10 where the permeable layer 12 is a geonet 14Cspaced between upper and lower geotextiles 14A and 14B with theperforated pipe 16 placed above the geonet 14C and showing the sensors40.

FIG. 4 is a schematic representation of a fluid injection and removalsystem 10 positioned on a top surface 120A of a contaminated area 120for injecting a waste treatment liquid 50 into the contaminated area 120showing the injected liquid front for time t₁ and the injected liquidfront for time t₂ is greater than t₁.

FIG. 5 is a schematic representation of a fluid injection and removalsystem 10 positioned on the surface 120A of a shallow contaminated area120 or waste for collecting and removing subsurface gases and vapors 52.

FIG. 6 is a schematic plan view of the fluid injection and removalsystems 10 of the Examples.

FIG. 7 is a schematic front view of the wetted front of the injectedliquid 50 in the permeable layer 12 and the simulated wetted width ofwaste W_(w) and the simulated wetted width of the permeable W_(B).

FIG. 8A is a graph of the simulated effect of the saturated hydraulicconductivity of solid waste k_(w) on the simulated wetted width, W_(B),and the pressure head of the injected liquid 50 in the permeable layer12 (PB) h_(p), overtime for k_(w) equal to 10⁻⁵ m/s, 10⁻⁶ m/s and 10⁻⁷m/s (3.3×10⁻⁵, 3.3×10⁻⁶ and 3.3×10⁻⁷ ft/s) for a liquid injection rate,Q, of 1.1 m³/hr/m.

FIG. 8B is a graph of the simulated effect of the saturated hydraulicconductivity of solid waste k_(w) on the simulated wetted width, W_(B),and the pressure head of the injected liquid 50 in the permeable layer12 (PB), h_(p), overtime for k_(w) equal to 10⁻⁵ m/s, 10⁻⁶ m/s and 10⁻⁷m/s for a liquid injection rate, Q, of 3.6 m³/hr/m.

FIG. 9A is a graph of the simulated effect of the saturated hydraulicconductivity of the permeable layer 12 k_(B), on the simulated wettedwidth, W_(B), and the pressure head of the injected liquid 50 in thepermeable layer 12 (PB), h_(p), overtime for k_(B) equal to 10⁻² m/s and10⁻³ m/s for a liquid injection rate, Q, of 1.1 m³/hr/m.

FIG. 9B is a graph of the simulated effect of the saturated hydraulicconductivity of the permeable layer 12, k_(B) on the simulated wettedwidth, W_(B), and the pressure head of the injected liquid 50 in thepermeable layer 12 (PB), h_(p), for k_(B) equal to 10⁻² m/s and 10⁻³ m/sfor a liquid injection rate, Q, of 3.6 m³/hr/m.

FIG. 10 is a graph of the effect of the thickness (depth) of thepermeable layer 12 on the simulated wetted width W_(B) and the pressurehead of the injected liquid 50 in the permeable layer 12, h_(p),overtime for a permeable layer 12 (PB) having a length of approximately60 m (200 ft), for the saturated hydraulic conductivity of the waste,k_(W), of 10⁻⁶ m/s, for a saturated hydraulic conductivity of thepermeable layer 12, k_(B), of 10⁻² m/s, for a liquid injection rate Q of1.1 m³/hr/m, for an initial degree of saturation of the permeable layer12, S_(B), of 50% and an initial degree of saturation of the waste,S_(W), of 45% for depths (thicknesses) of 0.45 m (1.47 ft) and 0.15 m(0.49 ft) for the permeable layer 12.

FIG. 11A is a graph of the simulated wetted width of waste, W_(W), as afunction of the dosing frequency for a permeable layer 12 having alength of 150 m for a liquid injection rate, Q, of 1.1 m³/hr/m, asaturated hydraulic conductivity of the waste, k_(W), of 10⁻⁶ m/s, asaturated hydraulic conductivity of the permeable layer 12 (PB), k_(B),of 10⁻² m/s, an initial degree of saturation of the permeable layer 12,S_(B), of 30% and an initial degree of saturation of the waste S_(W) of30%.

FIG. 11B is a graph of the simulated pressure head of injected liquid 50in the permeable layer 12 (PB), h_(p), as a function of the dosingfrequency for a permeable layer 12 having a length of 150 m for a liquidinjection rate, Q, of 1.1 m³/hr/m, a saturated hydraulic conductivity ofthe waste, k_(W), of 10⁻⁶ m/s, a saturated hydraulic conductivity of thepermeable layer 12, k_(B), of 10⁻² m/s, an initial degree of saturationof the permeable layer 12, S_(B), of 30% and an initial degree ofsaturation of the waste S_(W) of 30%.

FIG. 12A is a plot of the contours of the simulated maximum wetted widthof waste 100 at steady state as a function of the saturated hydraulicconductivity of the permeable layer 12, k_(B), and the saturatedhydraulic conductivity of waste 100, k_(W) for a constant injectionrate, Q, of 1.1 m³/hr/m.

FIG. 12B is a plot of the contours of the simulated maximum wetted widthof waste 100 at steady state as a function of the saturated hydraulicconductivity of the permeable layer 12, k_(B) and the saturatedhydraulic conductivity of the waste, k_(W) for a constant injectionrate, Q, of 3.6 m³/hr/m.

FIG. 13 is a graph of the simulated maximum wetted width of waste W_(W)at the end of daily leachate injection events as a function of theinitial degrees of saturation of waste 100, S_(W) and the permeablelayer 12, S_(B), for a permeable layer 12 having a length of 150 m(492.1 ft) for a liquid injection rate, Q, of 1.1 m³/hr/m for A hours onand 20 hours off, a saturated hydraulic conductivity of the permeablelayer, k_(B), of 10⁻² m/s and a saturated hydraulic conductivity ofwaste, k_(W), of 10⁻⁶ m/s.

FIG. 14 is a graph of the simulated wetted width, W_(B), and pressurehead of injected liquid 50 in a permeable layer 12 (PB), h_(p), as afunction of the degree of saturation of waste, S_(W), for a permeablelayer 12 having a length of approximately 60 m (200 ft) with a liquidinjection rate, Q, of 1.1 m³/hr/m, a saturated hydraulic conductivity ofthe permeable layer 12, k_(B), of 10⁻² m/s, a saturated hydraulicconductivity of waste, k_(W), of 10⁻⁶ m/s and an initial degree ofsaturation of the permeable layer 12, S_(B), of 50%.

FIG. 15 is a graph of the simulated wetted width, W_(B), and thesimulated pressure head of the injected liquid 50 in the permeable layer12 (PB), h_(p), versus the liquid injection period as a function of theinitial degree of saturation of the permeable layer 12, S_(B), for apermeable layer 12 having a length of approximately 60 m (200 ft) for aliquid injection rate, Q, of 1.1 m³/hr/m, a saturated hydraulicconductivity of waste, k_(W), of 10⁻⁶ m/s and an initial degree ofsaturation of the permeable layer 12, S_(B), of 45%.

FIG. 16 is a plot verifying the response of the impedance moisturecontent sensor 42 using a time domain reflectometry moisture contentsensor 44 for location E9 m in Example 3 overtime for an injection rate,Q, equal to 0.9 m³/hr/m for a leachate injection event having a durationof 0 to 125 min.

FIG. 17 is a plot showing the migration of leachate in the geocompositedrainage layer 14 of Example 3 as shown by the change in temperature andincrease in pressure head, h_(p), as measured by the sensors 40 atlocation E4.5 m (14.7 ft), for an injection rate, Q, of 2.6 m³/hr/m, anet injection pressure head, h_(I), of 400.0 cm (13.0 ft) overtime for aleachate injection event having a duration of 0 to 100 min.

FIG. 18A is a plot of the response of the impedance moisture contentsensors 42 in Example 3 at various sensor locations in the easternportion of the permeable layer 12 for a leachate injection event havinga duration of 0 to 125 minutes at a leachate injection rate equal to 0.9m³/hr/m.

FIG. 18B is a plot of the response of the impedance moisture contentsensors 42 in Example 3 at various sensor locations in the westernportion of the permeable layer 12 for a leachate injection event havinga duration of 0 to 125 minutes at a leachate injection rate equal to 0.9m³/hr/m.

FIG. 19 is a plot of the effect of the leachate injection rate on therate of travel of leachate in the permeable layer 12 for leachateinjection events corresponding to injection rates, Q, equal to 0.9 and2.6 m³/hr/m for Example 3.

FIG. 20 is a graph of the leachate injection pressure head and theleachate injection rate over time measured at the site for Example 3.

FIG. 21 is a graph of the leachate pressure heads and the temperatureswithin the permeable layer 12 and the waste temperature outside thepermeable layer 12 over time measured at the site for Example 3.

FIG. 22 is a plot indicating the arrival of leachate injected at aleachate injection rate, Q, of 140 gpm as shown by a decrease in theimpedance of the moisture sensors 42 for Example 1.

FIG. 23 is a plot indicating the arrival of leachate injected at aleachate injection rate, Q, of 45 gpm as shown by an increase in thepressure head h_(p) in the permeable layer 112 as measured by piezometersensors 46 for Example 1.

FIG. 24 is a plot indicating the arrival of leachate injected at aleachate injection rate, Q, of 140 gpm as shown by a decrease in theimpedance of the moisture sensors 42 for Example 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

The fluid injection and removal system 10 of the present inventionincludes a permeable layer 12 and a perforated pipe 16. The fluidinjection and removal system 10 is used to inject fluids 50 or 52 into aportion of solid waste 100 in a landfill 110, a landfill cell orcontaminated site and to remove fluids 50 or 52 including leachate,gases and vapors 52 from the solid waste 100, landfill cell orcontaminated site. The system 10 can be used to inject liquid 50 such aswater or gases such as air into the solid waste 100 or landfill cell toincrease the decomposition or degradation of the solid waste 100. Thesystem 10 can also be used to inject fluids into the solid waste 100,landfill cell or contaminated area 120 to treat the solid waste 100 orcontaminated area 120 for remediation of the solid waste 100 orcontaminated area 120.

The permeable layer 12 has a first surface 12A and an opposed secondsurface 12B forming a plane A-A of the permeable layer 12 (FIGS. 1A, 1Band 2). The permeable layer 12 has opposed ends 12C and 12D and opposedsides 12E and 12F with a length between the ends 12C and 12D and a widthbetween the sides 12E and 12F. The shape and size of the permeable layer12 can vary. When the system 10 is used to inject fluids into the solidwaste 100 of a landfill 110 or landfill cell or into a contaminated area120, the size and shape of the permeable layer 12 is determined based onthe recirculation or fluid injection needs of the solid waste 100 orcontaminated area 120, the shape of the solid waste 100 or contaminatedarea 120, the relative contrast in the hydraulic conductivity of thepermeable layer 12 and the underlying waste or contaminated area 120 andthe injection rate and pressure of the fluid.

In one (1) embodiment, the length of the permeable layer 12 between theends 12C and 12D is approximately between 30 m to 60 m (100 to 200 ft).The permeable layer 12 is constructed of a thin layer of permeablematerial having a high hydraulic conductivity. The depth or thickness ofthe permeable layer 12 between the first and second surface can varydepending upon the material used to construct the permeable layer 12,the design of the landfill site and the operational variables of thelandfill 110 and the permeable layer 12. A permeable layer 12constructed of a geocomposite material can have a thickness ofapproximately 10 mm (0.39 inches), whereas a permeable layer 12 made upof shredded tires can have thickness of 0.6 m (1.97 ft) depending on thesize of the tire shreds. The permeable layer 12 is constructed of amaterial having a hydraulic conductivity greater than the hydraulicconductivity of the underlying waste or the surrounding area or soil orthe contaminated area 120. The permeable layer 12 can be constructed ofcoarse sand, pea gravel, or granular recycled materials such as shreddedtires, crushed glass, or any material having a similar hydraulicconductivity. The hydraulic conductivity of crushed glass isapproximately 3×10⁻² m/s. The hydraulic conductivity of shredded rubbertires in Example 2 is approximately 0.1 m/s. In one (1) embodiment, thepermeable layer 12 is a geocomposite drainage layer 14 (FIGS. 2 and 3).A geocomposite drainage layer 14 is a flat geosynthetic blanket that isused in landfills 110 as well as other civil and environmental drainageapplications primarily as a leachate collection layer, a lead detectionlayer between primary and secondary liners of double lined landfills110, or as a lateral drainage layer to drain infiltrated precipitationin landfill caps (Koerner 1999). The geocomposite drainage layer 14includes a first or upper geotextile 14A and a second or lowergeotextile 14B with a geonet 14C sandwiched between the upper and lowergeotextile 14A and 14B (FIG. 3). A permeable layer 12 constructed as ageocomposite drainage layer 14 has good physical integrity againstdifferential loading or settlement and a relatively small thickness. Ageocomposite drainage layer 14 is constructed of a relatively hightransmissivity material. Under equivalent hydraulic conditions, a geonet14C having a thickness of 5 mm (0.19 inches) can be hydraulicallyequivalent to a gravel drainage layer having a thickness of betweenabout 200 and 300 mm (7.87 and 11.81 inches). Geotextiles can be placeddirectly above and below the permeable layer 12 constructed of anymaterial. The key purpose of geotextiles 14A and 14B is to separate thegeonet 14C or permeable layer 12 from the surrounding porous material(e.g., soil, waste, etc.) and to prevent clogging of the geonet 14C orpermeable layer 12. In one (1) embodiment, the lower geotextile 14Bextends upward along the sides 12E and 12F and ends 12C and 12D of thegeonet 14C or permeable layer 12. In one (1) embodiment, the lowergeotextile 14B is woven to reduce clogging of the permeable layer 12 orgeonet 14C. In one (1) embodiment, the upper geotextile 14A is non-wovento prevent the solid waste 100 from entering the permeable layer 12 orgeonet 14C. In one (1) embodiment, both the upper and lower geotextiles14A and 14B are non-woven.

The permeable layer 12 can be constructed of an inert material or areactive material. A reactive material is any material which removes orreduces the concentration of contaminants in the fluid 50 and 52 as thefluid 50 and 52 moves through the permeable layer 12. Any reactivematerial well known in the art such as carbon or iron filings can beused to construct the permeable material. U.S. Pat. No. 5,730,550 toAndersland et al which is incorporated herein in its entirety byreference describes the use of iron filings and microorganisms toconstructive reactive vertical barriers.

The fluid injection or removal system 10 includes at least oneperforated pipe 16. In one (1) embodiment, the perforated pipe 16 ispositioned adjacent to or embedded in the first surface 12A of thepermeable layer 12. However, the perforated pipe 16 can be positioned atany location adjacent the permeable layer 12 provided the perforatedpipe 16 is in fluid communication with the permeable layer 12. In theembodiment where the permeable layer 12 is a geocomposite drainage layer14, the perforated pipe 16 is positioned between the upper geotextile14A and the upper or first surface of the geonet 14C (FIG. 3). Multipleperforated pipes 16 can be used with a single permeable layer 12. In one(1) embodiment where the permeable layer 12 is a geocomposite drainage14, one of the perforated pipes 16 is positioned between the secondsurface of the geonet 14C and the lower geotextile 14B. The shape of theperforated pipe 16 depends on the shape of the permeable layer 12. Theperforated pipe 16 can be straight such as for use with a horizontal andlevel rectangular permeable layer 12 or can be spiral shaped or curvedsuch as for use with a circular permeable layer 12 or a permeable layer12 which is positioned on an uneven or curved surface. In one (1)embodiment, the perforated pipe 16 is constructed of high densitypolyethylene (HDPE). In one (1) embodiment, the perforated pipe 16 hasan inner diameter of approximately 0.075 m (0.246 ft). However, theinner diameter of the perforated pipe 16 depends on the amount of fluid50 or 52 to be injected or removed from the waste 100 or contaminatedsoil 124. The perforated pipe 16 has opposed ends. One end of theperforated pipe 16 is closed or capped off. In the embodiment where thesystem 10 is used to inject fluid 50 or 52, a pump 18 is connected tothe other end of the perforated pipe 16. In this embodiment, a flowcontrol valve 20, a pressure gauge 22 and a flow gauge 24 can bepositioned in the perforated pipe 16 to control and monitor the pressurehead and the flow rate of the injected fluid (FIG. 2). When the fluidinjection and removal system 10 is used to remove fluid from the wasteor contaminated site, a suction or vacuum system is connected to theother end of the perforated pipe 16. In one (1) embodiment, a storagecontainer 26 is connected to the perforated pipe 16, and the fluid ismoved to or from the perforated pipe 16 into or out of the storagecontainer 26.

The fluid injection and removal system 10 can be used in combinationwith a leachate collection system 30 to form a leachate recirculationsystem 130 (FIG. 1A). The leachate collection system 30 includes atleast one (1) perforated liquid recovery or collection pipe 32positioned in a layer of porous drainage material 34. The perforatedcollection pipe 32 has opposed ends with a cap at one end. A suction,vacuum or gravity driven removal system is attached to the other end ofthe collection pipe 32. The system 130 can also include a storagecontainer 26 for storing the leachate after removal. In one (1)embodiment, the collection pipe 32 is embedded in gravel as the drainagematerial 34. In one (1) embodiment, the hydraulic conductivity of theleachate collection system drainage material 34 K_(LCS) is approximatelyequal to 10⁻² m/s. In one (1) embodiment, the leachate collection system30 includes two (2) perforated collection pipes 32 having an innerdiameter of approximately 0.15 m (0.49 ft). In this embodiment, the two(2) collection pipes 32 are embedded in a layer of gravel approximately0.3 m (0.98 ft) thick at a horizontal spacing of approximately 60 m (200ft). In this embodiment, the slope of the leachate collection system 30is approximately equal to 3.5%. In one (1) embodiment, the leachatecollection system 30 includes a liner 36 which is positioned below theperforated collection pipe 32. In one (1) embodiment, the liner 36extends along the sides 12E and 12F and ends 12C and 12D of the waste100 and 102 forming a landfill cell. In one (1) embodiment, the liner 36is constructed of a non-porous material. In one (1) embodiment, thesuction or gravity driven removal system moves the recirculated leachatefrom the collection pipe 32 to the storage container 26. In one (1)embodiment, the recirculated leachate stored in the storage container 26is pumped into the perforated pipe 16 of the fluid injection system 10to be recirculated through the solid waste 100.

The fluid injection and removal system 10 is used in a portion of amunicipal solid waste landfill 110, landfill cell or contaminated area120 to inject liquids or gases into the solid waste 100 of the landfillor soil 124 contaminated area 120 or remove liquids or gases from thesolid waste 100 of the landfill 110 or the soil 124 of the contaminatedarea 120. In a bioreactive landfill 110, liquids or gases are injectedinto the waste to increase decomposition of the waste. However, liquidsand gases can also be injected into the waste to treat the waste such asto reduce the concentration of the contaminants in the waste. The fluidinjection system 10 can also be used on shallow contaminated soil 124 orimpacted ground for remediation of the contaminated area 120 or impactedground. Permeable layers 12 made of reactive materials can be used totreat ground water and release the ground water into subsurface. In one(1) embodiment, the permeable layer 12 is used to treat a shallow areawhere the soil 124 and/or ground water are contaminated at a depth lessthan or equal to 30 ft (FIG. 4). The permeable layer 12 can be used todeliver the appropriate chemicals or surfactants uniformly across theshallow contaminated zone 120 to wash the soil 124 or sediment particlesor to react with the ground water to clean the ground water (FIG. 4).

To use the fluid injection or removal system 10, the fluid injection orremoval system 10 is installed adjacent the solid waste 100 of thelandfill 110 or the contaminated soil 124 of the contaminated ground.The system 10 can be installed at any filling stage of a landfill 110before the landfill 110 is capped. Permeable layers 12 can be installedat various surface elevations within a solid waste landfill 110.Multiple fluid injection or removal systems 10 can be installed in alandfill 110 at different depths in the solid waste 100.

To install the fluid injection or removal system 10, the permeable layer12 is first positioned on the surface of the portion of the solid waste100 of the landfill 110 or the landfill cell or on top surface 120A ofthe contaminated area 120. In one (1) embodiment, the surface 120A ofthe solid waste 100 or contaminated area 120 is flattened and thepermeable layer 12 is inclined or sloped. In one (1) embodiment, thesurface 120A of the solid waste 100 or the contaminated area 120 isflattened to remove most bumps so that the permeable layer 12 isessentially flat. The permeable layer can be horizontal or along aninclined plane. The permeable layer 12 could also have a curved first orsecond surface 12A or 12B. The permeable layer 12 is positioned on thesolid waste 100 or contaminated area 120 so that the second or lowersurface 12B of the permeable layer 12 is adjacent the solid waste 100 orcontaminated soil 124. In the embodiment where the permeable layer 12 isa geocomposite drainage layer 14, the lower geotextile 14B is positionedon the surface 120A of the solid waste 100 or the contaminated area 120and the geonet 14C is positioned on the lower geotextile 14B on a sideopposite the solid waste 100 or contaminated area 120. In one (1)embodiment, a distance of greater than 15 m (49.2 ft) between the edgesof the permeable layer 12 and the side slopes of the landfill 110 wasmaintained to minimize the potential for leachate breakouts.

The perforated pipe 16 is then positioned adjacent the first surface 12Aof the permeable layer 12. The perforated pipe 16 can be positionedessentially along either the length or width of the permeable layer 12.However, it is more efficient to position the pipe 16 across or alongthe shorter dimension of the permeable layer 12. In one (1) embodiment,the perforated pipe 16 is parallel to either the sides 12E and 12F orthe ends 12C or 12D of the permeable layer 12. In one (1) embodiment,the perforated pipe 16 is parallel to the plane A-A of the permeablelayer 12. In one (1) embodiment, the perforated pipe 16 is positioned inthe center of the permeable layer 12 an equal distance from either theends 12C and 12D or the sides 12E and 12F of the permeable layer 12 soas to divide the permeable layer 12 into two (2) essentially identicalsegments. In one (1) embodiment, the perforated pipe 16 extends theentire length or width of the permeable layer 12.

After the fluid injection and removal system 10 is installed, additionalsolid waste 102 or soil 122 can be positioned on the first surface 12Aof the permeable layer 12 or on the upper geotextile 14A of thegeocomposite drainage layer 14.

Once the fluid injection or removal system 10 is installed, the pump 18is operated to inject or remove fluid into the perforated pipe 16 or thesuction or vacuum driven system is activated to remove fluid from theperforated pipe 16. Where the fluid injection or removal system 10 isused to inject fluid 50 or 52 into the solid waste 100 or contaminatedarea 120, the fluid 50 or 52 is injected under a positive pressure. Inone (1) embodiment, the fluid 50 is water. In one (1) embodiment, thefluid 50 is a waste treatment liquid. In one (1) embodiment, the fluidincludes surfactants. In one (1) embodiment, the fluid 50 isrecirculated leachate which has been treated and filtered. In one (1)embodiment, the fluid is a liquid which is injected at a liquidinjection rate Q of between about 0.9 m³/hr/m and 3.6 m³/hr/m per linearmeter length of the perforated pipe 16. In one (1) embodiment, theinjection is continuous. In another embodiment, the injection isconducted in on/off cycles. In the embodiment where the fluid injectionand removal system 10 is used to inject fluids into the solid waste 100or contaminated soil 124, the fluid exits the perforated pipe 16 andtravels through the permeable layer 12. The fluid 50 or 52 moves intothe solid waste 100 or contaminated soil 124 adjacent to or below thepermeable layer 12 after the fluid 50 or 52 moves through the permeablelayer 12. In one embodiment, the fluid 50 or 52 does not exit thepermeable layer 12 into the surrounding solid waste 100 or contaminatedsoil 124 until the permeable layer 12 is at least partially saturatedwith the fluid 50 or 52. The distance the fluid 50 or 52 moves in thepermeable layer 12 away from the perforated pipe 16 before exiting thepermeable layer 12 and moving into the adjacent waste 100 orcontaminated soil 124 depends on many factors including the hydraulicconductivity of the waste or underlying contaminated soil, the hydraulicconductivity of the permeable layer 12, the injection rate Q and thedosing frequency. The greater hydraulic conductivity of the permeablelayer 12 allows the fluid 50 or 52 to be distributed essentiallythroughout the permeable layer 12 before the fluid 50 or 52 moves fromthe permeable layer 12 to the adjacent solid waste 100 or contaminatedsoil 124. As the injected fluid infiltrates the permeable layer 12, thehigh hydraulic conductivity of the permeable layer 12 allowspreferential travel of the injected fluids within the permeable layer 12and wetting of the underlying waste 100 or soil 124. The distribution ofthe fluid essentially throughout the length and width of the permeablelayer 12 allows for a uniform distribution of the fluid into the wasteor ground below the permeable layer 12 throughout the entire area of thepermeable layer 12. Uniform distribution of the fluid in a landfill 110reduces uneven settlement of the solid waste 100 in the landfill 110 andincreases the gas generation potential of the landfill 110. In anotherembodiment, where the fluid injection and removal system 10 is used as agas removal system to remove gases 52 from the landfill 110 orcontaminated area 120, the suction or vacuum driven system is attachedto the end of the perforated pipe 16 opposite the capped end. The system10 is activated to collect and remove any gases or vapors 52 that havemoved into the perforated pipe 16 from the solid waste 100 orcontaminated ground 124 (FIG. 5). Permeable layers 12 can be usedindependently or in conjunction with vertical wells or horizontaltrenches to efficiently collect and gases or vapors 52. Use of permeablelayers 12 will cause significant reduction in gases or vapor emissionsfrom the ground surface and allow construction of buildings forindustrial applications at such sites.

To use the leachate recirculation system 130 in a municipal solid wastelandfill 110, the leachate collection system 30 is positioned at thebottom of the landfill 110. When the leachate collection system 30includes a liner 36 such as in a landfill cell, the liner 36 is firstpositioned on the bottom of the landfill 110 and then the drainagematerial 34 and the perforated collection pipe 32 are positioned on theliner 36 (FIG. 1A). The solid waste 100 is then positioned over theleachate collection system 30. The fluid injection and removal system 10is positioned in the solid waste 100 above the leachate collectionsystem 30 so that the leachate collection system 30 is spaced below andapart from the fluid injection and removal system 10. The spacing ordistance, D, between the fluid injection and removal system 10 and theleachate collection system 30 depends on site-specific factors (FIG.1A). The greater the distance, the better the decomposition of thelandfill 110 since the leachate is stored in the waste as it moves tothe leachate collection system 30. In one (1) embodiment, the fluidinjection and removal system 10 is spaced apart from the leachatecollection system 30 at least about 3.0 m (10 ft). In anotherembodiment, the distance, D, between the fluid injection and removalsystem 10 is approximately 3 m (10 ft). Additional solid waste 102 canbe positioned on the fluid injection and removal system 10 on a sideopposite the leachate collection system 30. Once the leachaterecirculation system 130 is installed, the hydraulic pump 18 isactivated to move the liquid 50 into the perforated pipe 16. In one (1)embodiment, the liquid 50 is water. In one embodiment, the liquid 50 isa waste treatment liquid. In one (1) embodiment, the liquid 50 isrecirculated leachate. The liquid 50 is moved into the perforated pipe16 under positive pressure and at an injection rate similar to theinjection rate of other liquids 50 using the fluid injection and removalsystem 10. The liquid 50 exits the perforated pipe 16 and enters thepermeable layer 12 and is distributed through the permeable layer 12.The liquid 50 exits the permeable layer 12 and enters the solid waste100. The rate of drainage of the injected liquid 50 through thepermeable layer 12 into the solid waste 100 is a function of thehydraulic conductivity of the permeable layer 12 and the underlyingsolid waste 100 and of the volume and frequency of the liquid injectionor dosing. The liquid 50 moves through the solid waste 100 toward theleachate collection system 30 due to gravity. The liquid or leachate 50enters the drainage material 34 of the leachate collection system 30 andenters the collection pipe 32 of the leachate collection system 30. Thesuction or gravity driven system is activated to remove the liquid orleachate 50 collected by the leachate collection system 30. The leachatecan be filtered and treated and stored in a storage container 26 to bereused in the leachate recirculation system 130. It is understood thatthe leachate could include solid particles and gases.

In one (1) embodiment, sensors 40 are mounted in the permeable layer 12adjacent to the second surface 12B of the permeable layer 12 (FIG. 3).Permeable layers 12 made up of granular materials provide an idealplatform to embed sensors 40. The permeable layer 12 having the sensors40 allows for a quick and efficient way to mount sensors 40 in the solidwaste 100 at different levels of the landfill 110. In one (1)embodiment, the sensors 40 include impedance moisture content sensors42, time domain reflectometry moisture content sensors 44, vibratingwire pressure transducers in the form of piezometers 46 and thermocoupleand thermistor temperature sensors 48. The sensors 40 monitor physical,chemical, or biological parameters associated with the migration ofinjected liquid, gases or leachate and the pressure and temperaturechanges in the permeable layer 12. Different sensors 40 can be operatedat different times which allows for more extensive data. Data collectedfrom the sensors 40 enables the estimation of hydraulic and thermalproperties and the change in the hydraulic and thermal properties of thesolid waste 100 or contaminated soil 124 directly below the permeablelayer 12 to be determined or estimated. The sensors 40 enable a user tocalculate the optimal operating temperature for landfills 110 or optimalliquid or fluid injection or recirculation rate. Using the data fromthese sensors 40 allows for more efficient design, construction andoperation of landfills 110.

In one (1) embodiment, a sensing and monitoring system can be used tomonitor the leachate injection rate and pressure and the rate of travelof injected leachate in the permeable layer 12. Such sensing andmonitoring systems can be used to manipulate the leachate injection rate(or pressure) to compensate for any differential settlement in thepermeable layer 12.

EXAMPLES

Three field-scale leachate recirculation permeable layers wereconstructed at an active municipal solid waste landfill. The landfillgenerates on average 45 m³ of leachate per day at the McGill Landfill inJackson, Mich. In Example 1, the permeable layer 112 was made up ofcrushed recycled glass. In Example 2, the permeable layer 212 wasconstructed of shredded tires. In Example 3, the permeable layer 312 wasa geocomposite drainage layer (FIG. 6). The first two (2) permeablelayers 112 and 212 had a length of about 55 m (180 ft) and a width ofabout 9 m (30 ft). The third permeable layer 312 had a length of about34 m (110 ft) and a width of about 12 m (40 ft) wide. A perforatedleachate injection pipe having a length of about 9 m (30 ft) and aninner diameter of 0.076 m (3 inches) was installed at the center of eachof the permeable layers 112, 212 and 312 in Examples 1 and 2 to injectleachate. The length of the pipe 16 was about 12 m (40 ft) for thepermeable layer 312 in Example 3. One (1) end of the perforated pipe wascapped and the other end was connected to a hydraulic pump. Thehydraulic pump was a high head/high discharge flow pump which was ableto pump up to 140 gpm at 100 ft of head. The hydraulic pump wasconnected to three (3) interconnected leachate storage tanks having atotal storage capacity equal to approximately 115 m³. A leachate flowcontrol valve, a digital pressure gauge, and a magnetic flow gauge werepositioned in the leachate injection perforated pipe to control andmonitor the pressure head and flow rate of the injected leachate.

The monitoring system included 30 moisture content sensors to detect thearrival of the leachate front and to monitor water balance of theleachate flow, 4 pressure head sensors (piezometers), 10 thermocouplesto measure the temperature of the leachate and the permeable layers. Aload sensor was also installed to measure the vertical stress from thewaste placed on the permeable layers. A pressure gauge was installed tomeasure leachate injection pressure and a magnetic flow meter was usedto measure leachate flux. A weather station or meteorological datasensors were used to measure precipitation, air temperature, andbarometric pressure.

Sensors were also installed to determine the physical characteristics,such as the hydraulic and thermal conductivities, or the change incharacteristics of the solid waste. In Examples 1 and 2, the sensorswere installed in the permeable layer 112 and 212 adjacent the second orbottom surface of the permeable layer 112 and 212. In Example 3 wherethe permeable layer 312 was a geocomposite drainage layer, the sensorswere installed in the solid waste immediately below the permeable layer.The sensors included 30 moisture content sensors, 4 piezometers; and 10thermocouples. The sensors were used to record the movement or migrationof liquid or leachate and to calculate the liquid or leachaterecirculation efficiency of the leachate recirculation system. A loadcell was also placed in the permeable layer or solid waste adjacent thepermeable layer. The load cell monitored the load on the permeable layerdue to solid waste placed on the permeable layer. A profiler conduit wasalso used to monitor settlement of the permeable layer. A digitalpressure gauge and a magnetic flow meter were installed adjacent theperforated pipe to monitor the liquid or leachate head and flow.Meteorological data sensors were also used.

The sensors were connected to an on-site Campbell CR10X datalogger and 3multiplexers to continuously log data. The frequency of data logging wasprogrammed at various intervals from once every minute to once every dayto capture the measurements.

Leachate recirculation trials were conducted on each of the threepermeable layers at leachate injection rates ranging from 15 to 140gallons per minute (gpm) (3.4 to 32 m³/hr). A leachate flow controlvalve was installed in the perforated pipe to control the leachate headand flow rate. The net injection pressure head ranged from about 0.6 to4 m (2 to 13 ft). The migration of leachate in the permeable layers 112,212 and 312 was monitored from the moisture contents measured aselectrical impedance, leachate temperature, and pressure head valuesmeasured by the sensors embedded in or immediately below the permeablelayer. The data established the relationship between the injection headand travel distance and showed that leachate travels horizontally in ashort period of time in a material that has hydraulic conductivitygreater than the waste in the landfill.

The data collected from the sensors indicated that in both permeablelayers, the leachate traveled across the entire length of the permeablelayer. The amount of time required for the leachate to travel across thepermeable layer varied from 10 minutes to over 90 minutes depending uponthe leachate flow rate. The collected data proved that, in landfillsoperated as bioreactors, a horizontal permeable layer made up of a highconductivity material is cost-effective and hydraulically efficient forrecirculation of leachate. The data may also be used to measure bulk insitu hydraulic conductivity of waste as an indicator of state ofdegradation of waste.

The location of the moisture sensor is identified by the distance of thesensor from the perforated leachate injection pipe installed at thecenter of the permeable layer (FIGS. 2 and 3). All moisture sensorsindicated that if leachate injection is paused, the water content of thepermeable layers decrease. Thus, the permeable layers can be used tocollect landfill gas without sucking in liquids from the landfill.

Based on the field data, leachate recirculation permeable layers made ofinert or reactive hydraulically permeable materials having a hydraulicconductivity or hydraulic transmissivity greater than the hydraulicconductivity of the underlying and overlying material (waste) can beused to recirculate leachate or liquids in landfills. The data alsoshowed that permeable layers distribute liquids more uniformly comparedto conventional trench or vertical well methods.

Example 1

In Example 1, where the permeable layer 112 was constructed of recycled,crushed glass, the permeable layer 112 had a thickness of about 0.15 m(0.5 ft).

The crushed recycled glass had an average particle diameter, D₅₀ ofapproximately 10 mm (0.394 inches). The permeable layer 112 had ahydraulic conductivity equal to 3×10⁻² m/s. The fluid injection andremoval system was constructed by first leveling the waste surface.Next, a non-woven lower geotextiles fabric was laid on the wastesurface. Below the lower geotextiles fabric, from top to bottom, was alayer of silty soil (loess) used as a daily soil cover having athickness or depth of about 50 mm (2 inches), a layer of municipal solidwaste having a thickness or depth of about 20 m (66 ft) and a leachatecollection and lining system. A layer of crushed glass having athickness or depth of about 0.15 m (0.49 ft) was placed on thegeotextiles to form the permeable layer 112. An upper geotextiles fabricwas then placed above the crushed glass. Additional waste having athickness or depth of about 3 m (10 ft) was placed on the uppergeotextiles fabric. A high density polyethylene (HDPE) leachateinjection perforated pipe having a length of about 9 m (30 ft) wasinstalled at the center of the permeable layer 112, parallel to thewidth, across the short side of the permeable layer 112.

The sensors for the monitoring system were installed in the crushedglass forming the permeable layer 112. The sensors were used to monitorthe travel of injected leachate in the permeable layer 112. No sensorswere installed in the underlying waste. The data logger was programmedto take readings at 1 to 5 minutes frequency to allow relatively precisemonitoring of the injected leachate and the pressure head of theinjected leachate in the permeable layer h_(p). For a period of abouteight (8) months, about 3,200 m³ of leachate was injected in thepermeable layer corresponding to approximately 90 leachate recirculationevents at leachate injection rates ranging from approximately 1.1 to 3.6m³/hour per meter length of the embedded injected perforated pipe. Themaximum leachate injection rate the pump at the site could deliver forthe total head that exists for the system was approximately 3.6 m³/hr/m.

The data from the impedance-based moisture sensors in response to theleachate injection in the permeable layer showed that for a leachateinjection rate of approximately 3.5 m³/hr/m, leachate traveled laterallyin the glass layer and reached the sensor located about 5 m (15 ft) tothe north of the injection pipe in about 7 minutes and reached about 27m (90 ft) in about 35 minutes (FIG. 22). The suffix “north” or “south”for the sensor location indicates which side of the perforated pipe thesensor is located. The data also showed that when the leachate injectionrate was reduced to approximately 1.1 m³/hr/m), the leachate traveledlaterally in the glass layer and reached the sensors located about 5 m(15 ft) to the north of the injection pipe in about 20 minutes andreached the sensors located at about 32 m (105 ft) in about 35 minutes.The data shows that leachate travel time in glass layer is linearlyproportional to the leachate injection rate. The liquid pressure headdata measured by the 3 piezometer sensors, installed in the glass layeron the south side, showed that liquid pressure in the glass layerincreased when the leachate injection was started (FIG. 23). Thepressure gradually reduced back to the original value once the leachateinjection was stopped. The data from the sensors showed that the liquidpressure in the glass layer increased and the temperature of the glasslayer decreased when the leachate injection was started. The temperatureof the leachate injected is less than the temperature of the permeablelayer before leachate injection was started.

Example 2

In Example 2, where the permeable layer 212 was constructed of shreddedtires, the permeable layer 212 had an average thickness of about 0.5 m(1.6 ft). The perforated pipe was constructed of HDPE and was installedat the center of the permeable layer across the short side or width ofthe permeable layer and had a length of about 9 m (30 ft).

The data showing the response of impedance-based moisture sensors to theleachate injection in the shredded tires layer, showed that for aleachate injection rate of approximately 3.5 m³/hr/m, the leachatetraveled laterally in the shredded tires layer and reached the sensorlocated at approximately 15 ft (4.57 m) to the north of the injectionpipe in about 2 to 3 minutes and reached the sensor located 23 to 27 m(75 to 90 ft) in about 20 to 25 minutes (FIG. 24). The data showed thatfor a leachate injection rate of 1.1 m³/hr/m), leachate traveledlaterally in the shredded tires layer and reached the sensors located atabout 9 m (30 ft) to the north of the perforated pipe in about 280minutes, reached the sensor located at about 14 m (45 ft) in about 60 to70 minutes, and reached the sensors located at about 18 to 27 m (60 to90 ft) in about 325 minutes. The data showed that the shredded tirelayer is linearly proportional to the leachate injection rate. In thepermeable layer constructed of shredded tires, due to the large size oftire shreds used, the flow within the shredded tire layer was not asuniform as in the glass layer. The sensors located farther from theleachate injection perforated pipe showed arrival of leachate earliercompared to sensors located near the perforated pipe.

Example 3

In Example 3, the permeable layer 312 was a geocomposite drainage layerto be used to recirculate leachate. Table 1 sets forth the keyproperties of the components of the geocomposite drainage layer.

TABLE 1 Physical Properties of the Geocomposite Drainage Layer UpperLower Component Geotextile Geotextile Geonet Type Non-Woven Woven —Thickness (mm) (ASTM 2 0.5 5 D 5199) Mass per Unit Area (g/m²) 270 200 —(ASTM D 5261) Transmissivity^(a) (cm²/s) — — 20 (ASTM D 4716-00)Permittivity (s⁻¹) 1.5 1.1 — (ASTM D 4491) Hydraulic Conductivity 0.30.05 — (cm/s) (ASTM D 4491) Apparent Opening Size 0.18 0.6 ~12.5 (mm)(ASTM D 4751) Percent Open Area (%) — 11 80 (CW- 02215) Note:^(a)gradient of 0.1, normal load of 480 kPa, water (permanent) at 20°C., between steel plates for 15 minutes.

Before placing the geocomposite drainage layer, the surface of thelandfill cell was essentially leveled. A topographic survey of thegeocomposite drainage layer conducted after the placement of thegeocomposite drainage layer indicated that the ground had an averageslope for east to southeast of about 3.5%. The landfill cell below thegeocomposite drainage layer included a first layer having an averagethickness of 0.05 m (16 ft) and containing silty soil (loess) used as adaily cover. A second layer below the first layer had a thickness ofabout 20 m (66 ft) and included municipal solid waste. A third and finallayer below the second layer included a leachate collection and liningsystem. The geocomposite drainage layer rolls were 4.6 m (15.1 ft) wide.The geocomposite drainage layer had a non-woven upper geotextile and awoven lower geotextile with the geonet spaced therebetween. Thenon-woven upper geotextile faced upward to prevent an intrusion of thewaste into the geonet. The woven lower geotextile faced downward tominimize potential clogging due to the underlying silt layer. To createa geocomposite drainage layer having a width of 12 m (39 ft), threegeocomposite drainage layer rolls were used with a 0.6 m (2.0 ft)overlap. In the overlap zone, the edges of the adjacent geonets werebutted against each other and an overlap of about 0.6 m (2.0 ft) wasused for the upper and lower geotextiles.

The perforated pipe was constructed of high density polyethylene (HDPE)and had a length of about 12 m (39 ft) and was installed at the centerof the geocomposite drainage layer, parallel to the width (FIG. 2). Theperforated pipe divided the geocomposite drainage layer into two almostidentical segments, a first or eastern segment and a second or westernsegment.

In this Example, the moisture content, temperature and pressure sensorswere embedded immediately below the geocomposite drainage layer in thesolid waste. A total of 14 locations adjacent the geocomposite drainagelayer were instrumented with impedance moisture content sensors, timedomain reflectometry moisture content sensors, vibrating wire pressuretransducers, and thermocouple and thermistor temperature sensors. Thesensors were installed immediately below the geocomposite drainage layer(FIG. 3). Holes measuring approximately 0.300 m (1 ft) in diameter andhaving a depth of about 0.300 m (1 ft) where excavated in the silty soillayer and waste below the geocomposite drainage layer and the sensor(s)were placed in drainage backfill consisting of coarse sand or crushedglass. The drainage backfill had a diameter D₅₀ Of approximately equalto about 0.012 m (0.039 ft), and a hydraulic conductivity ofapproximately 1 cm/s (0.39 in/s).

The impedance moisture content sensors measured the electrical impedanceR between two electrodes embedded in a sand pack having a diameter ofabout 50 mm (1.97 inches) (Gawande et al. 2003). The impedance of thesensor is inversely proportional to the moisture content of the sand orthe material surrounding the sand. A thermocouple of type T was added tothe impedance moisture content sensor to allow the measurement oftemperature.

The time domain reflectometry moisture content sensor measured thesurrounding medium's dielectric constant, which is directly related tothe moisture content. The time domain reflectometry sensor had a lengthof about 685 mm (26.9 inches) and a diameter of about 0.019 m (0.062ft).

The vibrating wire pressure transducer measured combined gas and liquidpressure. The pressure transducer was not vented and required correctionfor changes in the barometric pressure and temperature. A thermistor,attached to the pressure transducer, allowed measurement of thetemperature to correct the measurement of the transducer. Unlikethermocouple sensors, thermistors measured the absolute temperature anddid not require a reference temperature to make the measurements. Thetime domain reflectometry and impedance moisture content sensors werebackfilled with crushed glass and submerged in saline solutions havingelectrical conductivity ranging from 5 to 10 mS/cm. In one (1)embodiment, the crushed glass had an average particle diameter D₅₀ ofapproximately 12 mm (0.47 inches). Potassium chloride was used as anelectrolyte to adjust the electrical conductivity of the solutions. Therange of electrical conductivity represented the range of the electricalconductivity of injected leachate in the field. At saturation, the timedomain reflectometry readings ranged from 1230 to 1300 μA and theimpedance readings ranged from 0.02 to 0.03 kΩ.

A first sensor location, E4.5 m, included an impedance moisture contentsensor with a thermocouple, a time domain reflectometry moisture contentsensor, and a vibrating wire piezometer with a thermistor (FIG. 2). Theprefix of the location describes the location of the sensor with respectto the leachate injection pipe (e.g., NW, W, etc.) and the suffixrepresents the perpendicular distance from the leachate injection pipe(e.g., 4.5 m, 12 m, etc.) (FIG. 2). A second sensor location, E9 m,included an impedance moisture content sensor and a time domainreflectometry moisture content sensor. The use of different types ofsensors at the same location allowed for calibration and for independentverification of the data measured among the sensors.

A vertical pressure sensor was installed immediately outside one edge ofthe geocomposite drainage layer to monitor the weight (or verticalstress) of waste placed on the geocomposite drainage layer. The verticalpressure sensor also contained a thermistor which monitored thetemperature of the waste adjacent to the geocomposite drainage layer.Meteorological sensors including a rain gauge, an air temperaturesensor, and a barometric pressure sensor were also installed at thesite.

All sensors including the leachate flow gauge and pressure gauge wereconnected to a data logger located at the site. Most of the data wascollected at a 5-minute frequency to allow for precise monitoring of theinjected leachate.

During the 9 month monitoring period, about 1,800 m³ of leachate wasrecirculated in the geocomposite drainage layer corresponding toapproximately 27 leachate recirculation events. The leachate injectionrate, Q, ranged from about 0.9 m³ to about 2.6 m³ per hour per meterlength of the perforated pipe (m³/hr/m). The control valve was used toregulate the injection rate (FIG. 2). The maximum leachate rate wasapproximately 2.6 m³/hr/m which corresponded to the maximum rate thepump at the site could deliver at the total head that existed for thesystem. During the monitoring period, the rain gauge recorded about 5 m(16.5 ft) of cumulative precipitation at the site.

After the geocomposite drainage layer was covered with about 2 m (6.6ft) thick waste, leachate recirculation was started. The initialvertical stress recorded at the site was about 2 kPa. By the end of thetest period, the vertical stress increased to about 20 kPa due to wastefilling.

At the second sensor location E 9 m, data collected from the time domainreflectometry moisture content sensor was compared to data collectedfrom the impedance moisture content sensor (FIG. 16). In FIG. 16, thenegative values on the x-axis (−120 to 0) represent the time before theleachate injection started and the positive values on the x-axis (0 to240) represent the time after the leachate injection began (FIG. 16).The two arrows on the x-axis correspond to when the leachate injectionwas started and turned off. About 40 minutes after the start of theleachate injection at the second sensor location, E 9 m, the impedancestarted to drop and the time domain reflectometry reading started toincrease. This indicates an arrival of the wetting front of the injectedleachate. The impedance dropped from about 0.07 kΩ to 0.03 kΩ and thenstabilized. Similarly, the time domain reflectometry reading increasedfrom about 500 to 1,200 μA and then stabilized. The stabilized highreadings of the time domain reflectometry and impedance moisture contentsensors correspond to 100% saturation immediately below the geocompositedrainage layer. The data indicates temporary saturation of thegeocomposite drainage layer at the second sensor location E9 m due tothe leachate injection.

At the first sensor location E4.5 m, before the start of the leachateinjection, the temperature measured by the thermistor was about 24° C.and the pressure head measured by the transducer was about 10 cm (0.33ft) (FIG. 17). Leachate was injected at a rate equal to about 2.6m³/hr/m. The net leachate injection pressure head h_(i) in thegeocomposite drainage layer was estimated to be about 4 m (13.1 ft). Thenet leachate injection pressure head h_(i) in the geocomposite drainagelayer was estimated by subtracting head loss in the segment of theleachate injection pipe between the geocomposite drainage layer and theleachate pressure gauge located outside the geocomposite drainage layer.Moody's diagram (Moody 1944) was used to estimate the head loss. Theleachate injection pressure was measured using a pressure gauge locatedapproximately 40 m (131 ft) outside the geocomposite drainage layer(FIG. 2). The elevation of the leachate injection pressure measurementpoint was less than the average elevation of the geocomposite drainagelayer by about 100 cm (3 ft).

The temperature of the injected leachate was around 19° C. About 10 to15 minutes after the start of the leachate injection, in response to thearrival of the wetting front of the injected leachate, the temperaturemeasured by the thermistor decreased and simultaneously the pressurehead measured by the piezometer in the geocomposite drainage layerincreased.

Readings or data from the sensors at the first and second sensorlocations E4.5 m and E9 m were taken for a period of 6 hours whichincluded a period of 120 minutes before the beginning of the start ofthe leachate injection. In one (1) trial, data from the sensors at thefirst sensor location E4.5 m, was taken for a leachate injection rate of2.6 m³/hr/m for 100 minutes. In another trial, data from the sensors atthe second sensor location E9 m was taken for a leachate injection rateof 0.9 m³/hr/m for 125 minutes. No precipitation was recorded during theperiod the data was collected for either trial. The response of thesensors was strictly due to the leachate injected in the geocompositedrainage layer during those periods. The collected data indicated thatmoisture content, temperature, and pressure head, when measuredsimultaneously, can be used to monitor the migration of injectedleachate in or immediately below the permeable layer.

Data from the impedance moisture content sensors located in the twosegments of the geocomposite drainage layer was collected for leachateinjection events corresponding to a leachate injection rate Q equalapproximately to 0.9 m³/hr/m. The data showed that the impedancemoisture content sensors that were initially, partially saturated,experienced a decrease in impedance as the injected leachate reached thelocation of the sensor. However, those sensors that were initiallycompletely saturated did not show any decrease in impedance. Theresponse of the impedance moisture content sensors to a leachateinjection event where about 20 m³ of leachate was injected in thegeocomposite drainage layer over a 125 minute duration was recorded(FIGS. 18A and 18B). The injected leachate in the first or easternsegment of the geocomposite drainage layer reached the impedancemoisture content sensor at the first sensor location E4.5 m about 10minutes after the start of the leachate injection and reached theimpedance moisture content sensor at the second sensor location, E9 m,about 50 minutes after the start of the leachate injection. The injectedleachate reached the impedance moisture content sensor at a third sensorlocation, SE9 m about 20 minutes after the start of the leachateinjection, reached the impedance moisture content sensor at a fourthsensor location SE16 m (52.5 ft) about 60 minutes after the start of theleachate injection, and reached the impedance moisture content sensor ata fifth sensor location NE16 m within 120 minutes after the start of theleachate injection (FIG. 18A). The injected leachate in the second orwestern segment of the geocomposite drainage layer reached both theimpedance moisture content sensors at two locations NW14 m and W18 mabout 100 minutes after the start of the leachate injection (FIG. 18B).The rate of travel of injected leachate in the two segments of thegeocomposite drainage layer was not uniform. The leachate did reach thesensors located at the farthest locations SE 16 m, NE16 m, and W18 mfrom the perforated pipe in both segments of the geocomposite drainagelayer.

The arrival times of injected leachate at the various locations of thesensors in the two segments of the geocomposite drainage layer wasrecorded for leachate injection rates Q equal to about 0.9 and about 2.6m³/hr/m (FIG. 19). The arrival time was determined by the response ofimpedance moisture content sensors, located in the two segments of thegeocomposite drainage layer, to the arrival of injected leachate.

Moisture content sensors that were initially saturated were not able torecord the migration of injected leachate. Only sensors that wereinitially, partially saturated responded to the migration of injectedleachate. To ease the observation of the response of sensors, sensorslocated in the same direction (e.g., NE, E, SE, etc.) were clustered andassigned the same symbol. The arrival times for leachate injectionevents at leachate injection rate Q equal to about 0.9 and about 2.6m³/hr/m were recorded. The rate of travel of the injected leachate wasgreater for the higher leachate injection rate Q (FIG. 19). The averagerate of travel of injected leachate for leachate injection rates Q equalto 0.9 and 2.6 m³/hr/m, were also recorded (FIG. 19). The data indicatedan earlier arrival of injected leachate for the higher leachateinjection rate Q. For a leachate injection rate Q equal to about 0.9m³/hr/m, the injected leachate did not travel uniformly within the twosegments of the geocomposite drainage layer. For a leachate injectionrate Q equal to approximately 2.6 m³/hr/m, the travel of injectedleachate was more uniform.

Based on the arrival time of injected leachate at a given sensor, theinjected leachate traveled at an average rate of 5 to 10 m/hr (16.4 to32.8 ft/hr) in the geocomposite drainage layer for a leachate injectionrate Q equal to about 0.9 m³/hr/m and at an average rate of 12 to 18m/hr (39.4 to 59.0 ft/hr) for a leachate injection rate Q equal to about2.6 m³/hr/m. The rate of travel of injected leachate for a givenleachate injection rate was not uniform across the geocomposite drainagelayer due to preferential flow in the geocomposite drainage layer,wrinkles formed in the geocomposite drainage layer during installation,spatial variation of the hydraulic conductivity and moisture content ofthe underlying waste, and the slight slope of approximately 3.5% of thewaste surface. Wrinkles formed in the geocomposite drainage layer as aresult of the unevenness of the waste surface on which the geocompositedrainage layer was laid and thermal stresses induced from a few days ofsun exposure before the geocomposite drainage layer was covered withwaste.

Potential clogging of the geotextiles in the geocomposite drainage layeris one of the key operational concerns for permeable layer made ofgeocomposite drainage layer. If the geocomposite drainage layerpartially clogs, the injection head must be increased to maintain theleachate injection rate. As the leachate injection head increases, theliquid pressure head in the geocomposite drainage layer and itsimmediate vicinity also increases.

For leachate injection rates equal to about 0.9, 1.4, and 2.6 m³/hr/m,the leachate injection pressures were about 200, 400, and 800 cm (78.7,157.5, 314.9 inches), respectively. For a given injection rate, leachateinjection pressure readings were constant and did not increasethroughout the monitoring period (FIG. 20). Total hydraulic frictionloss in the perforated pipe having a non-perforated length of about 40 m(131 ft) and perforated length equal to about 12 m (39 ft) long wasestimated using Moody's diagram. For leachate injection rate rangingfrom about 0.9 to 2.6 m³/hr/m, the total friction loss ranged from about100 to 300 cm (39 to 118 inches). Thus, the net leachate injectionpressures (h_(i)) ranged from about 50 to 400 cm (20 to 158 inches).

For each leachate injection event, both the pressure transducer and thethermistor located at the first sensor location E4.5 m responded to thearrival of the injected leachate (FIG. 21). The pressure transducerrecorded an increase in leachate pressure head as the pore waterpressure increased due to the arrival of injected leachate. The increasein the pressure head gradually dissipated after the leachate injectionwas stopped. A pressure head h_(p) with a magnitude of about 30 cm (12inches) was recorded for a leachate injection rate of about 0.9 m³/hr/m.A pressure head with a magnitude of about 80 cm (32 inches) was recordedfor a leachate injection rate of about 2.6 m³/hr/m (FIG. 21).

A comparison of the leachate injection pressure and the leachatepressure head below the geocomposite drainage layer at the first sensorlocation E4.5 m indicates that significant leachate pressure head lossoccurs as the injected leachate travels through the geocompositedrainage layer. During the monitoring period, the pressure head measuredat the first sensor location E4.5 m never exceeded the injectionpressure head.

The temperature of the geocomposite drainage layer was also affected byleachate recirculation. The temperature in the geocomposite drainagelayer temporarily decreased due to the arrival of injected leachate.This occurred because the temperature of the injected leachate wasalmost always less than the temperature of the geocomposite drainagelayer. The temperature of the waste monitored using the vertical stresssensor located immediately outside the one edge of the geocompositedrainage layer was approximately equal to or greater than thetemperature recorded at the first sensor location E4.5 m (FIG. 21). Thevariation of the seasonal air temperature had a relatively small effecton the temperature of the geocomposite drainage layer due to the thermalinsulation provided by the waste mass.

The sensors showed that the rate flow of injected leachate in thegeocomposite drainage layer is a function of the leachate injectionrate, the extent of wrinkles present in the geocomposite drainage layerbefore it is covered, the slope of the geocomposite drainage layer, andthe degree heterogeneity in the hydraulic properties of underlyingwaste. During use, excess pressures were not developed in the vicinityof the geocomposite drainage layer indicating that the geocompositedrainage layer provided hydraulic continuity. The moisture contentsensors embedded immediately below the geocomposite drainage layer weresaturated during leachate injection demonstrating that the geocompositedrainage layer transported the leachate. No clogging of the geocompositedrainage layer was apparent during the 9 month test period as indicatedby no change in the injection pressure for a given injection rate orduring the 20 month monitoring period.

Simulation 1

The simulation shows the effect of the hydraulic properties of the wasteand the permeable layer, the geometry of the permeable layer, thesettlement of the permeable layer, the leachate dosing frequency, andthe degree of saturation of the waste and the permeable layer on thehydraulic performance of permeable layers.

The simulation shows that to maintain a minimum liquid pressure build upin the permeable layer and to achieve the greatest wetted width in thepermeable layer, the permeable layer should be constructed of a materialhaving a high hydraulic conductivity. The simulation further shows thatan increase in the thickness or depth of the permeable layer decreasesthe pressure head in the permeable layer, h_(p). A permeable layerhaving a greater thickness is preferable if slope stability evaluationof the landfill requires lower pressure heads in the permeable layer. Athicker layer does not result in a greater wetted width of the waste anddoes not offer greater wetting of the underlying waste. Furthermore, thesimulation shows that the greater the hydraulic conductivity of theunderlying waste, the lower the wetted width W_(B) and the lower thepressure head in the permeable layer h_(p).

The simulation also shows that the greater the degrees of saturation ofthe waste and/or the permeable layer, the faster the rate of travel ofinjected leachate in the permeable layer and greater the pressure headin the permeable layer h_(p). When leachate is injected in on/off dosingcycles, the initial degree of saturation of waste S_(W) and the initialdegree of saturation of the permeable layer S_(B) increase until asteady-state approaches. The wetted width of waste W_(W) and pressurehead in the permeable layer h_(p) are directly proportional to the on tooff duration ratio and the magnitude of the liquid flux during the onperiod. In addition, the simulation shows that if the permeable layersettles, a greater leachate injection rate (or head) is needed tocompensate for the loss in elevation head to maintain the same thesaturated wetted width of waste, W_(W).

The HYDRUS-2D computer model is used for the simulation to develop aconceptual model to numerically evaluate the use of permeable layers asa leachate recirculation system (FIG. 1). HYDRUS-2D is a computer modelthat can simulate water, heat, and solute movement or migration inunsaturated, partially saturated, or fully saturated porous media(Simunek, J., et al., The HYDRUS-2D Software Package for Simulating the2-D Movement of Water, Heat, and Multiple Solutes in Variable SaturatedMedia, Version 2.0. U.S. Salinity Laboratory, Agriculture ResearchService, USDA, Riverside, Calif. (1999)). The program numerically solvesthe Richards' Equation for saturated and unsaturated water flow. A 2-Dform of Richards' equation can be expressed as follows:

$\frac{\partial\theta}{\partial t} = {{{- \nabla} \cdot \left\lbrack {{k(\psi)} \cdot {\nabla\psi}} \right\rbrack} + \frac{\partial k}{\partial z} - S}$

where, θ=volumetric water content; ψ=matric suction head; k=hydraulicconductivity, which is k_(S) for saturated soil but is stronglydependent on the soil suction; z=vertical dimension; S=volume of waterremoved per unit time per unit volume of soil by plant water uptake(sink term); and t=time.

The model uses van-Genuchten function for soil-water characteristiccurves and van-Genuchten-Mualem model for predicting the unsaturatedhydraulic conductivity function. The governing flow and transportequations are numerically solved using Galerkin-type linearfinite-element schemes. Depending upon the scale of the problem domain,the matrix equations resulting from the discretization of the governingequations are solved using either Gaussian elimination for bandedmatrices, a conjugate gradient method for symmetric matrices, or theORTHOMIN method for asymmetric matrices.

In this simulation, the municipal solid waste is assumed to be ahomogeneous and isotropic porous medium having k_(W) ranging from 10⁻⁷m/s to 10⁻⁵ m/s (3.3×10⁻⁷ to 3.3×10⁻⁵ ft/s). The effect of channeling isnot considered. An average saturated hydraulic conductivity of waste,k_(W) equal to 10⁻⁶ m/s (3.3×10⁻⁶ ft/s) is used in most simulations.These values are selected according to typical values published byHughes et al. (1971); Fungaroli and Steiner (1979); Korfiatis et al.(1984); Oweis et al. (1990) and Bleiker et al. (1993).

The conceptual model includes a fluid injection system and a leachatecollection system. The fluid injection system includes a permeable layerhaving a thickness of approximately 0.015 m (0.049 ft) and a perforatedpipe having an inner diameter of approximately 0.1 m (0.33 ft). Theperforated pipe is positioned through the center of the permeable layeressentially parallel to the plane formed by the permeable layer. Thelength of the permeable layer has a range between about 55 m to 150 m(180 ft and 492 ft). The vertical distance, D, between the permeablelayer and the top of the leachate collection system ranges from about 5m to 20 m (16 ft to 66 ft). The distance from the top of the permeablelayer to the upper, zero flux boundary is approximately 5 m (16 ft).This distance allow for containment of all injected leachate andprevents possible artesian conditions for the simulated leachateinjection rates. The leachate collection system includes two (2)perforated collection pipes having an inner diameter of 0.15 m (0.49ft). The perforated collection pipes are embedded in a gravel layerhaving a thickness of 0.3 m (1 ft) and have a horizontal spacing, d,equal to approximately 60 m (196.8 ft). The slope (tan β) of theleachate collection system is equal to 3.5% (FIG. 1A). The hydraulicconductivity of the leachate collection system drainage material(k_(LCS)) is equal to 10⁻² m/s. The leachate collection system designparameters (t_(LCS), k_(LCS), d, and tan β) result in less than 0.3 mleachate pressure head on the lining system for all simulations.

The saturated and unsaturated hydraulic properties of the simulatedwaste, the permeable layer material, and the leachate collection systemgravel layer which are input into HYDRUS-2D are set forth in Table 2.

TABLE 2 Saturated and unsaturated hydraulic properties ResidualSaturated Dimension- Saturated Volumetric Volumetric less HydraulicWater Water Fitting Fitting Conductivity Landfill Content ContentParameter Parameter k_(s) Unit Material θ_(r) θ_(s) α (1/m) N (m/s)Waste Silt 0.078 0.45 3.6 1.54 10⁻⁵, 10⁻⁶ and loam 10⁻⁷ Permeable Pea0.01 0.3 57.4 2.44 10⁻² and 10⁻³ Layer gravel Permeable Crushed 0.020.47 12 5 3 × 10⁻² Layer Glass Leachate Pea 0.01 0.3 57.4 2.44 10⁻²Collection gravel System

The leachate is simulated as pure water. Any reference to leachate flowcorresponds to water flow. The results of the simulation can be appliedto any injected liquids for bioreactor landfills as long as the liquid'sphysical and hydraulic properties are similar to that of water. Theeffect of gas flow, temperature and biochemical reactions occurringwithin the landfill are ignored.

All external boundaries are simulated as zero flux boundaries. Theperforated pipe of the fluid injection system is simulated as a constantflux boundary. The flux (dimensions: M⁰L¹T⁻¹) assigned to the boundaryis calculated by dividing the leachate injection rate (dimensions: M⁰L³T⁻¹) by the perimeter of the perforated pipe of the fluid injectionsystem for a unit length of the perforated pipe. The leachate injectionrates (Q) range from 1.1 to 3.6 m³/hr/m. These rates are selected basedon leachate injection rates used in the field for permeable layerstested in this study and other studies. The maximum leachate injectionrate of 3.6 m³/hr/m corresponds to the maximum rate the pump used in thesimulation could deliver for the total head that existed for the system.The leachate injection rates Q in m³/hr/m represents the leachateinjection rate in cubic meters per hour per linear meter length of thepipe. The collection pipes embedded in the leachate collection systemare simulated as seepage face boundaries. Leachate flow as a result ofpercolation from the cap or waste above the model domain is assumed tobe zero.

The dosing cycles for leachate recirculation range from 2 hours on and22 hours off to 8 hours on and 16 hours off to cover various dosingvolumes and frequencies for a typical municipal solid waste landfill.Leachate injection is simulated as constant flux under a positiveleachate injection pressure.

The wetted width is the distance traveled by the injected leachate fromthe perforated pipe of the fluid injection system (FIG. 7). The wettedwidth of waste, W_(W) and the saturated wetted width of the permeablelayer, W_(B) are different (FIG. 7). The wetted width of waste, W_(W) isdefined as the maximum distance traveled by the injected leachate fromthe perforated pipe in the permeable layer just above the underlyingwaste. The wetted width of waste, W_(W) dictates the lateral extent ofinfiltration of the injected leachate through the underlying waste. Thesaturated wetted width of the permeable layer, W_(B) is defined as theone-half (½) of the length of the permeable layer where the entire depth(thickness) of the permeable layer is 100% saturated (FIG. 7). For afully saturated permeable layer having a length of approximately 60 m(196.8 ft), the saturated wetted width of the permeable layer, W_(B) is30 m (98.4 ft). The saturated wetted width of the permeable layer W_(B)is always less than wetted width of waste W_(W). The difference betweenwetted width of waste W_(W) and the saturated wetted width of thepermeable layer W_(B) varies depending upon the leachate injection rate,the thickness of the permeable layer and the hydraulic properties of thepermeable layer and waste.

The injected leachate temporarily increases the degree of saturation ofthe permeable layer and the pressure head in the permeable layer h_(p).One key parameter that impacts the shear strength of the waste is theeffective stress. The pressure head distribution in the permeable layeris a key factor for slope stability analysis of bioreactor landfills.The pressure head in the permeable layer h_(p), is simulated bymeasuring the pressure head in the proximity or within 0.5 m (1.6 ft) ofthe perforated pipe at the bottom of the permeable layer (FIG. 1B). Thepressure head in the permeable layer h_(p) is always greater near theperforated pipe. The pressure head in the permeable layer h_(p) isdifferent from the injection pressure head, h_(i) inside the perforatedpipe. The pressure head in the permeable layer h_(p) is a function ofthe leachate injection rate and the hydraulic properties of permeablelayer and waste. It is believed that the pressure head in the permeablelayer, h_(p), can be used to interpret and monitor the hydraulicperformance of the leachate recirculation system. For example, if themagnitude of the pressure head h_(p) is close to the injection pressurehead h_(i), then there is good hydraulic continuity between theperforated pipe and the permeable layer. An increase in the differencebetween the injection pressure head h_(i) and the pressure head of thepermeable layer h_(p) over time for a given magnitude of leachateinjection rate, indicates a decrease in the hydraulic conductivity ofthe permeable layer or potential clogging of the perforated pipe.

Over 150 simulations using HYDRUS-2D were conducted to evaluate theeffect of the hydraulic properties of the waste, the geometry of thepermeable layer, the hydraulic properties of the permeable layer, thesettlement of the permeable layer, the leachate dosing volume andfrequency, and the degree of saturation of the waste and the permeablelayer on the wetted width and pressure head of injected leachate in thepermeable layer.

Unless specified otherwise, all simulations use a permeable layer havinga length of approximately 60 m (196.8 ft) and a thickness or depth of0.15 m (0.49 ft). The permeable layer has an initial degree ofsaturation S_(B) of 50%. The initial degree of saturation of waste S_(W)is 45%. The hydraulic properties of the permeable layer are those of peagravel with a saturated hydraulic conductivity k_(B) 10⁻² m/s. Thehydraulic properties of the solid waste are those of loam fromHYDRUS-2D's database with a saturated hydraulic conductivity k_(W) of10⁻⁶ m/s. The vertical spacing or distance between the permeable layerand the leachate collection system D is 5 m.

To evaluate the effect of unsaturated hydraulic properties of municipalsolid waste on the wetted width of waste W_(W) and the pressure head inthe permeable layer h_(p), the municipal solid waste is simulated assand and loam in two separate simulations. The saturated hydraulicconductivities of sand and loam are assigned a value of 10⁻⁶ m/s.Different soil-water characteristic curves are assigned for sand andloam from the HYDRUS-2D database. In the first simulation, leachate wascontinuously injected at an injection rate equal to 1.1 m³/hr/m for aninjection period of 8 hours. In the second simulation, leachate wasinjected in dosing cycles of 4 hours on and 20 hours off for a totalperiod of 7 days. The initial degrees of saturation for the permeablelayer and the solid waste were equal for all simulations. Theunsaturated hydraulic properties of loam were used for all simulations,unless it is specified otherwise. The results indicate that unsaturatedhydraulic properties of the waste are critical only for short termanalysis (less than 2 or 3 days). For long-term and recurring leachateinjection analysis, unsaturated hydraulic properties of the materialused to simulate municipal solid waste have virtually no influence onthe wetted width and the pressure head of injected leachate in thepermeable layer.

The effect of the saturated hydraulic conductivity of waste k_(W) on thesimulated saturated wetted width of the permeable layer W_(B) and thepressure head of the permeable layer h_(p) in a permeable layer having alength of approximately 60 m (196.8 ft) was simulated (FIGS. 8A and 8B).The values of the saturated hydraulic conductivity of waste k_(W) were10⁻⁵, 10⁻⁶, and 10⁻⁷ m/s (3.3×10⁻⁵, 3.3×10⁻⁶, 3.3×10⁻⁷ ft/s). Thesimulated values are the typical reported values for municipal solidwaste. In one simulation, the leachate injection rate Q is 1.1 m³/hr/mfor an injection period of 8 hours (FIG. 8A). In another simulation, theleachate injection rate Q is 3.6 m³/hr/m for an injection period of 3hours (FIG. 8B). For a saturated hydraulic conductivity of waste k_(W)of 10⁻⁵ m/s (3.3×10⁻⁵ ft/s), the simulated saturated wetted width of thepermeable layer W_(B) is 6 m (20 ft) after 8 hours of continuousleachate injection The simulated pressure head in the permeable layerh_(p) remained below 0.3 m (0.98 ft) throughout the leachate injectionperiod. For a saturated hydraulic conductivity of waste k_(W) of 10⁻⁷m/s (3.3×10⁻⁷ ft/s), the saturated wetted width of the permeable layerW_(B) reaches the maximum possible value of 30 m (98.4 ft) after 6 hoursof continuous leachate injection for a permeable layer having a lengthof approximately 60 m (196.8 ft). The pressure head in the permeablelayer h_(p) rises as the injected leachate travels within the permeablelayer and increases the degree of saturation of the permeable layer.Once the injected leachate reaches a distance of 30 m (98.4 ft), and theentire permeable layer is saturated, the pressure head in the permeablelayer h_(p) increases sharply as the storage capacity of the permeablelayer is exceeded. The increase in the pressure head h_(p) is greaterwhere the underlying municipal solid waste has a lower hydraulicconductivity.

For a saturated hydraulic conductivity of waste k_(W) of 10⁻⁵ m/s(3.3×10⁻⁵ ft/s), the simulated saturated wetted width of the permeablelayer W_(B) is about 17 m (55.8 ft) after an injection period of 3 hoursfor a leachate injection rate Q of 3.6 m³/hr/m compared to about 6 m(19.7 ft) for a leachate injection rate Q of 1.1 m³/hr/m after aninjection period of 8 hours (FIG. 8B). The simulated pressure head inthe permeable layer h_(p) is 1.5 m (4.9 ft) for a leachate injectionrate Q of 3.6 m³/hr/m. The pressure head in the permeable layer h_(p) is0.3 m (0.98 ft) for a leachate injection rate Q of 1.1 m³/hr/m. For asaturated hydraulic conductivity of waste k_(W) of 10⁻⁶ and 10⁻⁷ m/s(3.3×10⁻⁶ and 3.3×10⁻⁷ ft/s), the saturated wetted width of thepermeable layer W_(B) is 30 m (98.4 ft) after an injection period of 2.5and 1.5 hours, respectively.

The saturated hydraulic conductivity of the permeable layer k_(B) variesdepending on the permeable material used to construct the permeablelayer. A greater hydraulic conductivity is preferable when selecting amaterial for the permeable layer. The effect of the saturated hydraulicconductivity of the permeable layer, k_(B) on the simulated saturatedwetted width of the permeable layer W_(B) and the pressure head in thepermeable layer h_(p) for a permeable layer having a length ofapproximately 60 m (196.8 ft) for a saturated hydraulic conductivity ofwaste k_(W) of 10⁻⁶ m/s was simulated (FIG. 9). The effect of thesaturated hydraulic conductivity of the permeable layer material k_(B)on the saturated wetted width of the permeable layer W_(B) and thepressure head in the permeable layer h_(p) is simulated using saturatedhydraulic conductivity k_(B) values equal to 10⁻² and 10⁻³ m/s. Theleachate injection rate Q is 1.1 m³/hr/m for an injection period of 8hours (FIG. 9A) and 3.6 m³/hr/m for an injection period of 3 hours (FIG.9B). The injected leachate travels at a slower rate for permeable layershaving a lower saturated hydraulic conductivity k_(B) and results in agreater pressure head in the permeable layer h_(p) for a given leachateinjection rate.

To simulate the effect of the depth or thickness of the permeable layeron the wetted width and pressure head of injected leachate in thepermeable layer, two simulations are conducted using permeable layerthickness values of 0.15 m (0.49 ft) and 0.45 m (1.47 ft). The saturatedhydraulic conductivity of waste k_(W) is equal to 10⁻⁶ m/s (3.3×10⁻⁶ft/s) and the leachate injection rate Q is equal to 1.1 m³/hr/m for aninjection period of 8 hours. Simulation results indicate that thesaturated wetted width of the permeable layer W_(B) decreases as thepermeable layer depth increases (FIG. 10). However, the wetted width ofwaste W_(W) does not differ significantly between the two differentdepths of the permeable layer. As the depth of permeable layerincreases, the storage capacity of the permeable layer increased. Theincrease in storage capacity results in a lower h_(p) for the thickerpermeable layer. A thinner permeable layer is preferable to reduce thecost of constructing the permeable layer. A thicker permeable layer ispreferable to keep the pressure head of the permeable layer h_(p) in anacceptable range for slope stability concerns.

The effect of the length of the permeable layer on the saturated wettedwidth of the permeable layer W_(B) is evaluated by simulating twopermeable layers having different lengths. Permeable layers havinglengths of approximately 60 m (196.8 ft) and 150 m (492.1 ft) are used.In the simulations, the saturated hydraulic conductivity of waste k_(W)is equal to 10⁻⁶ m/s (3.3×10⁻⁶ ft/s) and the leachate injection rate Qis equal to 1.1 m³/hr/m. The injection period is 8 hours. The simulationresults indicate that the permeable layer length has no effect on thewetted width of the waste W_(W) or the saturated wetted width of thepermeable layer W_(B) or the leachate pressure head h_(p).

The effect of vertical spacing between the permeable layer and theleachate collection system is evaluated by simulating a vertical spacingD equal to 5 m (16.4 ft) and 20 m (65.6 ft). The saturated hydraulicconductivity of waste k_(W) is equal to 10⁻⁶ m/s (3.3×10⁻⁶ ft/s) and theleachate injection rate Q is equal to 1.1 m³/hr/m for an injectionperiod of 8 hours. The simulation results indicate that D does notinfluence the wetted width or the leachate pressure head h_(p).

The effect of the settlement of waste and the settlement of thepermeable layer on leachate flow through the permeable layer issimulated. The composition of waste, climate, presence or absence ofleachate recirculation, and other physical and biochemical factorsimpact the settlement of waste in landfills. Due to the differentialsettlement of waste, permeable layers constructed within waste will alsoundergo differential settlement. Settlement of waste in landfills hasbeen reported to range from 10% to 30% of its initial thickness. Theeffect of settlement of waste on the leachate flow through a permeablelayer having a length of approximately 60 m (196.8 ft) is evaluated bysimulating a 3 m (10 ft) deep sag at the center of the permeable layer.The 3 m (10 ft) deep sag represents differential settlement equal to 3 m(10 ft). The simulation results indicate that for leachate injectionpressure heads less than the magnitude of the simulated sag, theleachate flux is less than that for a horizontal permeable layer and theinjected leachate can not fill up the entire permeable layer. Theleachate injection rate needs to be increased to create an additionalinjection pressure head that can compensate for the sag. Once theinjection pressure head was greater than or equal to the magnitude ofthe sag, the leachate flux is essentially equal to the leachate flux fora horizontal permeable layer, the injected leachate fills up the entirepermeable layer resulting in a greater wetted width of waste W_(W) and agreater saturated wetted width of the permeable layer, W_(B).

Simulations are conducted to determine the effect of dosing frequency onthe wetted width of waste W_(W). For the simulation, the leachateinjection rate Q is equal to 1.1 m³/hr/m. The simulation is conductedfor leachate injection dosing frequencies of 2 hours on and 22 hoursoff, 4 hours on and 20 hours off, and 8 hours on and 16 hours off. Wherethe saturated hydraulic conductivity of waste k_(W) is equal to 10⁻⁶ m/s(3.3×10⁻⁶ ft/s) and the initial degree of saturation of waste S_(W) andthe initial degree of saturation of the permeable layer S_(B) are equalto 30%, the wetted width of waste W_(W) is a function of the ratio of onto off leachate injection duration (FIG. 11A). The wetted width ofwaste, W_(W) is greater for a dosing cycle where the on to off timesratio is greater. For a given dosing frequency, the wetted width ofwaste W_(W) increases as the number of leachate dosing days increasesuntil the wetted width of waste W_(W) reaches a constant maximum valueranging from 15 to 45 m (49 to 148 ft) depending on the on to offduration ratio after almost ten days (FIG. 11A).

The pressure head of injected leachate in the permeable layer h_(p) forthe dosing frequencies of 2 hours on and 22 hours off and 4 hours on and20 hours off is also measured (FIG. 11B). For a given dosing frequency,the pressure head of injected leachate in the permeable layer h_(p)increases and then remains almost constant as the leachate dosingcontinues and the system almost reaches a steady-state. The initialincrease is due to the increase in the degree of saturation of the wasteand the permeable layer. The magnitude of the pressure head of injectedleachate in the permeable layer h_(p) is a function of the on to offduration ratio. The greater the on to off duration ratio, the greater,the magnitude of the pressure head of injected leachate in the permeablelayer h_(p).

Simulation is also used to evaluate the effect of continuous leachateinjection (until steady-state is reached) on the wetted width of wasteW_(W) to obtain the maximum possible wetted width for a given leachateinjection rate. The wetted width of waste W_(W) for a permeable layerhaving a length of 150 m (492 ft) using continuous leachate injection ata leachate injection rate Q equal to 1.1 m³/hr/m (FIG. 12A) and aleachate injection rate Q equal to 3.6 m³/hr/m (FIG. 12B) is measured asa function of the saturated hydraulic conductivity of waste k_(W) andthe saturated hydraulic conductivity of the permeable layer materialk_(B). The saturated hydraulic conductivity of waste k_(W) varied from10⁻⁷ m/s (3.3×10⁻⁷ ft/s) to 10⁻⁵ m/s (3.3×10⁻⁵ ft/s) and the saturatedhydraulic conductivity of the permeable layer material k_(B) varied from10⁻⁴ m/s (3.3×10⁻⁴ ft/s) to 10⁻² m/s (3.3×10⁻² ft/s) during thesimulation. The simulated wetted width of waste W_(W) is mainly afunction of saturated hydraulic conductivity of waste k_(W) as long asthe saturated hydraulic conductivity of the permeable layer materialk_(B) is greater than the saturated hydraulic conductivity of wastek_(W). The simulated maximum wetted width of waste W_(W) increases asthe saturated hydraulic conductivity of waste k_(W) decreases. Eitherincreasing the leachate injection rate Q or reducing the saturatedhydraulic conductivity of waste k_(W) can increase the wetted width ofwaste W_(W).

A simulation is used to determine the rate of travel of injectedleachate in a permeable layer as a function of the initial degrees ofsaturation of the waste S_(W) and of the permeable layer S_(B). Theeffect of initial conditions S_(W) and S_(B) on the simulated wettedwidth of waste W_(W) for a permeable layer having a length of 150 m (492ft) where the saturated hydraulic conductivity of waste k_(W) is equalto 10⁻⁶ m/s 93.3×10⁻⁶ ft/s) and the leachate injection rate Q is equalto 1.1 m³/hr/m for a dosing frequency of 4 hours on and 20 hours off aremeasured (FIG. 13). Four possible sets of initial conditions are usedwith the initial degree of saturation of waste S_(W) ranging from 30% to65% and the initial degree of saturation of the permeable layer S_(B)ranging from 30% to 95%. The range of initial degrees of saturation isselected based on the typical range of values observed in the field forbioreactor landfills. For all four sets of simulations, the wetted widthof waste W_(W) increases as the number of leachate dosing daysincreases. However, irrespective of the initial degrees of saturation ofthe waste and the permeable layer, the maximum wetted width of wasteW_(W) is about the same after a few days (long-term) of leachate dosingfor a set leachate injection rate Q and dosing frequency. It takes aprogressively longer time to reach the maximum wetted width of wasteW_(W) for lower initial degrees of saturation S_(W) and S_(B) (FIG. 13).

A simulation is used to determine the effect the degree of saturation ofwaste plays in operating an efficient bioreactor landfill. The effect ofthe initial degree of saturation of waste is evaluated by simulatinginitial degree of saturation of waste S_(W) values equal to 30%, 45%,and 65%. Porosity of the waste is equal to 0.45, the initial degree ofsaturation of waste S_(W) values correspond to volumetric water contentsranging from 0.15 to 0.3 units. The effect of the initial degree ofsaturation of waste S_(W) on the saturated wetted width of the permeablelayer W_(B) and the pressure head of the injected leachate in thepermeable layer h_(p) in a permeable layer having a length ofapproximately 60 m (196.8 ft) for a saturated hydraulic conductivity ofwaste k_(W) equal to 10⁻⁶ m/s (3.3×10⁻⁶ ft/s) and a leachate injectionrate Q equal to 1.1 m³/hr/m over a period of 8 hours of continuousleachate injection is measured. The initial degree of saturation of thepermeable layer S_(B) is maintained at 50% for all simulations. Theresults show that the greater the initial degree of saturation of wasteS_(W), the faster the rate of travel of the injected leachate (FIG. 14).When the leachate injection is continued beyond 8 hours, the saturatedwetted width of the permeable layer W_(B) and the wetted width of wasteW_(W) reach a maximum value that is about the same for various initialdegree of saturation of waste S_(W) values indicating that asteady-state is reached.

The degree of saturation of the permeable layer varies and depends uponthe rate, duration and frequency of leachate dosing cycle, infiltrationof precipitation, and the hydraulic properties of the surrounding wasteand permeable layer. The initial degree of saturation of the permeablelayer S_(B) varies significantly over the operational life of thepermeable layer. The effect of the initial degree of saturation of thepermeable layer S_(B) on the saturated wetted width of the permeablelayer W_(B) and the pressure head of the injected leachate in thepermeable layer h_(p) in a permeable layer having a length ofapproximately 60 m (196.8 ft) for a saturated hydraulic conductivity ofwaste k_(W) equal to 10⁻⁶ m/s (3.3×10⁻⁶ ft/s) and the leachate injectionrate Q equal to 1.1 m³/hr/m during an injection period of 8 hours ismeasured (FIG. 15). The simulated values of the initial degree ofsaturation of the permeable layer S_(B) are equal to 30%, 65%, and 95%.The initial degree of saturation of waste S_(W) is constant at 45%. Theinjected leachate travels faster for a greater initial degree ofsaturation of the permeable layer S_(B) (FIG. 15). The difference in therate of travel of the injected leachate for the various values of theinitial degree of saturation of the permeable layer S_(B) is small. Thesimulated pressure head of the injected leachate in the permeable layerh_(p) differs only slightly for the various values of the initial degreeof saturation of the permeable layer S_(B).

The simulation also shows that as the injection head is increased, theleachate flux increases a permeable layer. The relationship islog-linear for permeable layer for injection heads greater than thebreakthrough pressure head. The leachate flux linearly increases with anincrease in the length of the permeable layer. The increase in thehydraulic conductivity of permeable layer material results in increasein leachate flux. However, for hydraulic conductivities greater than orequal to 5×10⁻³ m/s 16.4×10⁻³ ft/s), the difference is negligible.

It is intended that the foregoing description be only illustrative ofthe present invention and that the present invention be limited only bythe hereinafter appended claims.

1-24. (canceled)
 25. A system for injecting fluid into a portion ofsolid waste in a landfill which comprises: (a) a layer constructed of apermeable material having a hydraulic conductivity and having a firstsurface and an opposed second surface forming a plane of the layer,wherein the layer is configured to be positioned on the portion of solidwaste in the landfill so that the second surface of the layer isadjacent the solid waste; and (b) a perforated pipe positioned adjacentthe layer parallel to the plane of the layer, wherein fluid is injectedinto the perforated pipe and moves from the perforated pipe into thelayer and travels through the layer and into the portion of solid wasteadjacent the second surface of the layer.
 26. The system of claim 25wherein the layer has opposed ends and opposed sides with a lengthbetween the ends and a width between the sides, wherein the perforatedpipe is positioned along the width of the layer so as to inject fluidalong an entire width of the layer and wherein the permeable materialhas a hydraulic conductivity greater than the hydraulic conductivity ofthe portion of solid waste adjacent the layer so that the fluid travelsthrough the length of the layer before a significant amount of the fluidexits the layer into the portion of solid waste adjacent the layer sothat distribution of the fluid into the solid waste is essentiallyuniform along the length and width of the layer.
 27. The system of claim26 wherein the perforated pipe is positioned in the layer an equaldistance from each of the ends of the layer and parallel to the ends ofthe layer so that the perforated pipe divides the layer into twoessentially equal segments extending along the length of the layer. 28.The system of claim 25 wherein the fluid is a liquid and a flow controlvalve, a pressure gauge and a flow gauge are connected to the perforatedpipe to control and monitor fluid pressure head and fluid flow rate inthe perforated pipe.
 29. The system of claim 25 wherein the permeablematerial is shredded rubber tires, pea gravel or crushed glass or anymaterial which has a hydraulic conductivity greater than a hydraulicconductivity of the portion of solid waste adjacent the layer.
 30. Thesystem of claim 25 wherein the layer is constructed of a geocompositedrainage layer which includes a first geotextile, a second geotextileand a geonet layer spaced between the first and second geotextiles. 31.The system of claim 30 wherein the second geotextile is constructed of awoven material to minimize clogging of the layer due to the solid waste.32. The system of claim 30 wherein the first geotextile is constructedof a non-woven material to prevent solid waste positioned from movinginto the geonet.
 33. The system of claim 25 wherein the layer has athickness between the first and second surface of at least about 0.01 mand 0.6 m.
 34. The system of claim 25 wherein when the layer issaturated, the hydraulic conductivity of the layer is between about3×10⁻² and 10⁻³ m/s.
 35. The system of claim 25 wherein the fluid iswaste treatment liquid and wherein the layer is constructed of areactive material and the waste treatment liquid reacts with the layerto reduce contaminants in the waste treatment liquid.
 36. The system ofclaim 25 wherein sensors are mounted in the layer adjacent the secondsurface of the layer.
 37. The system of claim 36 wherein the sensors aremoisture content sensors, temperature sensors and pressure sensors. 38.A system for collecting and recirculating waste treatment liquid in aportion of solid waste in a landfill which comprises: (a) a layerconstructed of a permeable material having a hydraulic conductivity andhaving a first surface and an opposed second surface forming a plane ofthe layer, the layer configured to be positioned on the portion of solidwaste in the landfill so that the second surface of the layer isadjacent the solid waste of the landfill; (b) a perforated pipepositioned adjacent the layer parallel to the plane of the layer; and(c) a waste treatment liquid collection system including at least oneperforated collection pipe embedded in a layer of hydraulicallyconductive material, wherein the waste treatment liquid collectionsystem is positioned in the portion of solid waste of the landfilladjacent to and spaced apart from the second surface of the layer,wherein the waste treatment liquid is injected into the layer throughthe perforated pipe and travels through the layer and is distributedinto the solid waste adjacent the second surface of the layer and movesdownward through the portion of solid waste toward the waste treatmentliquid collection system due to gravity and moves through thehydraulically conductive material of the waste treatment liquidcollection system and into the perforated collection pipe.
 39. Thesystem of claim 38 wherein a suction or gravity driven system isconnected to the perforated collection pipe to move the recirculatedwaste treatment liquid from the perforated collection pipe into astorage container.
 40. The system of claim 39 wherein a hydraulic pumpis connected between the storage container and the perforated pipe tomove the recirculated waste treatment liquid from the storage containerinto the perforated pipe and into the layer.
 41. The system of claim 38wherein the waste treatment liquid collection system includes a linerwhich is positioned on a side of the perforated collection pipe oppositethe layer. 42-46. (canceled)